diff --git a/src/graphql/BaseResolver.ts b/src/graphql/BaseResolver.ts
new file mode 100644
index 0000000..753af99
--- /dev/null
+++ b/src/graphql/BaseResolver.ts
@@ -0,0 +1,17 @@
+import {NotLoggedInGqlError} from "../lib/errors/graphqlErrors";
+
+/**
+ * Base resolver class to provide common methods to all resolver classes
+ */
+export abstract class BaseResolver {
+
+    /**
+     * Checks if the user is logged in and throws an exception if not
+     * @param request
+     */
+    protected ensureLoggedIn(request: any) {
+        if (!request.session.userId) {
+            throw new NotLoggedInGqlError();
+        }
+    }
+}
diff --git a/src/graphql/BlacklistedResult.ts b/src/graphql/BlacklistedResult.ts
new file mode 100644
index 0000000..4139424
--- /dev/null
+++ b/src/graphql/BlacklistedResult.ts
@@ -0,0 +1,6 @@
+export class BlacklistedResult {
+    constructor(
+        public blacklisted: boolean,
+        public phrases: string[],
+    ) {}
+}
diff --git a/src/graphql/MutationResolver.ts b/src/graphql/MutationResolver.ts
index 017f822..f70de4d 100644
--- a/src/graphql/MutationResolver.ts
+++ b/src/graphql/MutationResolver.ts
@@ -1,6 +1,467 @@
+import {GraphQLError} from "graphql";
+import * as yaml from "js-yaml";
+import isEmail from "validator/lib/isEmail";
+import dataaccess from "../lib/dataAccess";
+import {BlacklistedError} from "../lib/errors/BlacklistedError";
+import {GroupNotFoundError} from "../lib/errors/GroupNotFoundError";
+import {InvalidEmailError} from "../lib/errors/InvalidEmailError";
+import {NotAGroupAdminError} from "../lib/errors/NotAGroupAdminError";
+import {NotAnAdminError} from "../lib/errors/NotAnAdminError";
+import {NotTheGroupCreatorError} from "../lib/errors/NotTheGroupCreatorError";
+import {PostNotFoundError} from "../lib/errors/PostNotFoundError";
+import globals from "../lib/globals";
+import {InternalEvents} from "../lib/InternalEvents";
+import {Activity, BlacklistedPhrase, ChatMessage, ChatRoom, Event, Group, Post, Request, User} from "../lib/models";
+import {BaseResolver} from "./BaseResolver";
+
+const legit = require("legit");
+
 /**
  * A class that provides methods to resolve mutations
  */
-export class MutationResolver {
+export class MutationResolver extends BaseResolver {
+
+    /**
+     * Accepts the usage of cookies and stores the session
+     * @param args
+     * @param request
+     */
+    public acceptCookies(args: null, request: any): boolean {
+        request.session.cookiesAccepted = true;
+        return true;
+    }
+
+    /**
+     * Loggs in and appends the user id to the session
+     * @param email
+     * @param passwordHash
+     * @param request
+     */
+    public async login({email, passwordHash}: { email: string, passwordHash: string }, request: any): Promise<User> {
+        const user = await dataaccess.getUserByLogin(email, passwordHash);
+        request.session.userId = user.id;
+        return user;
+    }
+
+    /**
+     * Loggs out by removing the user from the session
+     * @param args
+     * @param request
+     */
+    public logout(args: null, request: any) {
+        this.ensureLoggedIn(request);
+        delete request.session.userId;
+        request.session.save((err: any) => {
+            if (err) {
+                globals.logger.error(err.message);
+                globals.logger.debug(err.stack);
+            }
+        });
+    }
+
+    /**
+     * Registers a new user account
+     * @param username
+     * @param email
+     * @param passwordHash
+     * @param request
+     */
+    public async register({username, email, passwordHash}: { username: string, email: string, passwordHash: string },
+                          request: any): Promise<User> {
+        let mailValid = isEmail(email);
+        if (mailValid) {
+            try {
+                mailValid = (await legit(email)).isValid;
+            } catch (err) {
+                globals.logger.warn(`Mail legit check returned: ${err.message}`);
+                globals.logger.debug(err.stack);
+                mailValid = false;
+            }
+        }
+        if (!mailValid) {
+            throw new InvalidEmailError(email);
+        }
+        const user = await dataaccess.registerUser(username, email, passwordHash);
+        request.session.userId = user.id;
+        return user;
+    }
+
+    /**
+     * Sets the frontend settings for the logged in user
+     * @param settings
+     * @param request
+     */
+    public async setUserSettings({settings}: { settings: string }, request: any): Promise<string> {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        try {
+            user.frontendSettings = yaml.safeLoad(settings);
+            await user.save();
+            return user.settings;
+        } catch (err) {
+            throw new GraphQLError("Invalid settings json.");
+        }
+    }
+
+    /**
+     * Toggles a vote of a specific type on a post and returns the post and the result
+     * @param postId
+     * @param type
+     * @param request
+     */
+    public async vote({postId, type}: { postId: number, type: dataaccess.VoteType }, request: any):
+        Promise<{ post: Post, voteType: dataaccess.VoteType }> {
+        this.ensureLoggedIn(request);
+        const post = await Post.findByPk(postId);
+        if (post) {
+            const voteType = await post.vote(request.session.userId, type);
+            return {
+                post,
+                voteType,
+            };
+        } else {
+            throw new PostNotFoundError(postId);
+        }
+    }
+
+    /**
+     * Creates a new post
+     * @param content
+     * @param activityId
+     * @param request
+     */
+    public async createPost({content, activityId}: { content: string, activityId?: number }, request: any):
+        Promise<Post> {
+        this.ensureLoggedIn(request);
+        if (content.length > 2048) {
+            throw new GraphQLError("Content too long.");
+        }
+        const post = await dataaccess.createPost(content, request.session.userId, activityId);
+        globals.internalEmitter.emit(InternalEvents.GQLPOSTCREATE, post);
+        return post;
+    }
+
+    /**
+     * Deletes a post if the user is either the author or a site admin.
+     * @param postId
+     * @param request
+     */
+    public async deletePost({postId}: { postId: number }, request: any): Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const post = await Post.findByPk(postId, {
+            include: [{
+                as: "rAuthor",
+                model: User,
+            }],
+        });
+        const isAdmin = (await User.findOne({where: {id: request.session.userId}})).isAdmin;
+        if (post.rAuthor.id === request.session.userId || isAdmin) {
+            return await dataaccess.deletePost(post.id);
+        } else {
+            throw new GraphQLError("User is not author of the post.");
+        }
+    }
+
+    /**
+     * Creates a chat with several members
+     * @param members
+     * @param request
+     */
+    public async createChat({members}: { members?: number[] }, request: any): Promise<ChatRoom> {
+        this.ensureLoggedIn(request);
+        const chatMembers = [request.session.userId];
+        if (members) {
+            chatMembers.push(...members);
+        }
+        return await dataaccess.createChat(...chatMembers);
+    }
+
+    /**
+     * Sends a message into a chat the user has joined
+     * @param chatId
+     * @param content
+     * @param request
+     */
+    public async sendMessage({chatId, content}: { chatId: number, content: string }, request: any):
+        Promise<ChatMessage> {
+        this.ensureLoggedIn(request);
+        const message = await dataaccess.sendChatMessage(request.session.userId, chatId, content);
+        globals.internalEmitter.emit(InternalEvents.GQLCHATMESSAGE, message);
+        return message;
+    }
+
+    /**
+     * Sends a request to a specific user
+     * @param receiver
+     * @param type
+     * @param request
+     */
+    public async sendRequest({receiver, type}: { receiver: number, type: dataaccess.RequestType }, request: any):
+        Promise<Request> {
+        this.ensureLoggedIn(request);
+        return dataaccess.createRequest(request.session.userId, receiver, type);
+    }
+
+    /**
+     * Denies a request
+     * @param sender
+     * @param type
+     * @param request
+     */
+    public async denyRequest({sender, type}: { sender: number, type: dataaccess.RequestType }, request: any) {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        await user.acceptRequest(sender, type);
+        return true;
+    }
+
+    /**
+     * Accepts a request
+     * @param sender
+     * @param type
+     * @param request
+     */
+    public async acceptRequest({sender, type}: { sender: number, type: dataaccess.RequestType }, request: any) {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        await user.acceptRequest(sender, type);
+        return true;
+    }
+
+    /**
+     * Removes a friend
+     * @param friendId
+     * @param request
+     */
+    public async removeFriend({friendId}: { friendId: number }, request: any): Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        return user.removeFriend(friendId);
+    }
+
+    /**
+     * Creates a new group
+     * @param name
+     * @param members
+     * @param request
+     */
+    public async createGroup({name, members}: { name: string, members: number[] }, request: any): Promise<Group> {
+        this.ensureLoggedIn(request);
+        return await dataaccess.createGroup(name, request.session.userId, members);
+    }
+
+    /**
+     * Deletes a group if the user is either the creator or a site admin
+     * @param groupId
+     * @param request
+     */
+    public async deleteGroup({groupId}: { groupId: number }, request: any): Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        const group = await Group.findByPk(groupId);
+        if (group) {
+            if (user.isAdmin || group.creatorId === user.id) {
+                await group.destroy();
+                return true;
+            }
+        } else {
+            throw new GroupNotFoundError(groupId);
+        }
+    }
+
+    /**
+     * Joins a group
+     * @param groupId
+     * @param request
+     */
+    public async joinGroup({groupId}: { groupId: number }, request: any): Promise<Group> {
+        this.ensureLoggedIn(request);
+        return dataaccess.changeGroupMembership(groupId, request.session.userId,
+            dataaccess.MembershipChangeAction.ADD);
+    }
+
+    /**
+     * Leaves a group
+     * @param groupId
+     * @param request
+     */
+    public async leaveGroup({groupId}: { groupId: number }, request: any): Promise<Group> {
+        this.ensureLoggedIn(request);
+        return dataaccess.changeGroupMembership(groupId, request.session.userId,
+            dataaccess.MembershipChangeAction.REMOVE);
+    }
+
+    /**
+     * Adds a user to the group admins
+     * @param groupId
+     * @param userId
+     * @param request
+     */
+    public async addGroupAdmin({groupId, userId}: { groupId: number, userId: number }, request: any): Promise<Group> {
+        this.ensureLoggedIn(request);
+        const group = await Group.findByPk(groupId);
+        const user: User = await User.findByPk(request.session.userId);
+        if (group && !(await group.$has("rAdmins", user)) && (await group.creator()) !== user.id) {
+            throw new NotAGroupAdminError(groupId);
+        }
+        return dataaccess.changeGroupMembership(groupId, userId,
+            dataaccess.MembershipChangeAction.OP);
+    }
+
+    /**
+     * Removes an admin from a group
+     * @param groupId
+     * @param userId
+     * @param request
+     */
+    public async removeGroupAdmin({groupId, userId}: { groupId: number, userId: number },
+                                  request: any): Promise<Group> {
+        this.ensureLoggedIn(request);
+        const group = await Group.findByPk(groupId);
+        const isCreator = Number(group.creatorId) === Number(request.session.userId);
+        const userIsCreator = Number(group.creatorId) === Number(userId);
+        if (group && !isCreator && Number(userId) !== Number(request.session.userId)) {
+            throw new NotTheGroupCreatorError(groupId);
+        } else if (userIsCreator) {
+            throw new GraphQLError(
+                "You are not allowed to remove a creator as an admin.");
+        }
+        return await dataaccess.changeGroupMembership(groupId, userId,
+            dataaccess.MembershipChangeAction.DEOP);
+    }
+
+    /**
+     * Creates a new event for a specific group
+     * @param name
+     * @param dueDate
+     * @param groupId
+     * @param request
+     */
+    public async createEvent({name, dueDate, groupId}: { name: string, dueDate: string, groupId: number },
+                             request: any): Promise<Event> {
+        this.ensureLoggedIn(request);
+        const date = new Date(Number(dueDate));
+        const user: User = await User.findByPk(request.session.userId);
+        const group = await Group.findByPk(groupId, {include: [{association: "rAdmins"}]});
+        if (!(await group.$has("rAdmins", user))) {
+            throw new NotAGroupAdminError(groupId);
+        }
+        const blacklisted = await dataaccess.checkBlacklisted(name);
+        if (blacklisted.length > 0) {
+            throw new BlacklistedError(blacklisted.map((p) => p.phrase), "event name");
+        }
+        return group.$create<Event>("rEvent", {name, dueDate: date});
+    }
+
+    /**
+     * Deletes an event
+     * @param eventId
+     * @param request
+     */
+    public async deleteEvent({eventId}: { eventId: number }, request: any): Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const event = await Event.findByPk(eventId, {include: [Group]});
+        const user = await User.findByPk(request.session.userId);
+        const group = await event.group();
+        if (await group.$has("rAdmins", user)) {
+            await event.destroy();
+            return true;
+        } else {
+            throw new NotAGroupAdminError(group.id);
+        }
+    }
+
+    /**
+     * Joins an event
+     * @param eventId
+     * @param request
+     */
+    public async joinEvent({eventId}: { eventId: number }, request: any): Promise<Event> {
+        this.ensureLoggedIn(request);
+        const event = await Event.findByPk(eventId);
+        const self = await User.findByPk(request.session.userId);
+        await event.$add("rParticipants", self);
+        return event;
+    }
+
+    /**
+     * Leaves an event
+     * @param eventId
+     * @param request
+     */
+    public async leaveEvent({eventId}: { eventId: number }, request: any): Promise<Event> {
+        this.ensureLoggedIn(request);
+        const event = await Event.findByPk(eventId);
+        const self = await User.findByPk(request.session.userId);
+        await event.$remove("rParticipants", self);
+        return event;
+    }
+
+    /**
+     * Creates a new activity or throws an error if the activity already exists
+     * @param name
+     * @param description
+     * @param points
+     * @param request
+     */
+    public async createActivity({name, description, points}: { name: string, description: string, points: number },
+                                request: any): Promise<Activity> {
+        this.ensureLoggedIn(request.session.userId);
+        const user = await User.findByPk(request.session.userId);
+        if (!user.isAdmin) {
+            throw new NotAnAdminError();
+        }
+        const nameExists = await Activity.findOne({where: {name}});
+        if (!nameExists) {
+            return Activity.create({name, description, points});
+        } else {
+            throw new GraphQLError(`An activity with the name '${name}' already exists.`);
+        }
+    }
+
+    /**
+     * Adds a phrase to the blaclist
+     * @param phrase
+     * @param languageCode
+     * @param request
+     */
+    public async addToBlacklist({phrase, languageCode}: {phrase: string, languageCode?: string}, request: any):
+        Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        if (!user.isAdmin) {
+            throw new NotAnAdminError();
+        }
+        const phraseExists = await BlacklistedPhrase.findOne(
+            {where: {phrase, language: languageCode}});
+        if (!phraseExists) {
+            await BlacklistedPhrase.create({phrase, language: languageCode});
+            return true;
+        } else {
+            return false;
+        }
+    }
 
+    /**
+     * Removes a phrase from the blacklist
+     * @param phrase
+     * @param languageCode
+     * @param request
+     */
+    public async removeFromBlacklist({phrase, languageCode}: {phrase: string, languageCode: string}, request: any):
+        Promise<boolean> {
+        this.ensureLoggedIn(request);
+        const user = await User.findByPk(request.session.userId);
+        if (!user.isAdmin) {
+            throw new NotAnAdminError();
+        }
+        const phraseEntry = await BlacklistedPhrase.findOne(
+            {where: {phrase, language: languageCode}});
+        if (phraseEntry) {
+            await phraseEntry.destroy();
+            return true;
+        } else {
+            return false;
+        }
+    }
 }
diff --git a/src/graphql/QueryResolver.ts b/src/graphql/QueryResolver.ts
index 51a9828..91b94b6 100644
--- a/src/graphql/QueryResolver.ts
+++ b/src/graphql/QueryResolver.ts
@@ -1,5 +1,196 @@
+import {GraphQLError} from "graphql";
+import {Op} from "sequelize";
+import dataaccess from "../lib/dataAccess";
+import {ChatNotFoundError} from "../lib/errors/ChatNotFoundError";
+import {PostNotFoundGqlError} from "../lib/errors/graphqlErrors";
+import {GroupNotFoundError} from "../lib/errors/GroupNotFoundError";
+import {InvalidLoginError} from "../lib/errors/InvalidLoginError";
+import {RequestNotFoundError} from "../lib/errors/RequestNotFoundError";
+import {UserNotFoundError} from "../lib/errors/UserNotFoundError";
+import {
+    Activity,
+    BlacklistedPhrase,
+    ChatRoom,
+    Event,
+    Group,
+    Post,
+    Request,
+    User,
+} from "../lib/models";
+import {BaseResolver} from "./BaseResolver";
+import {BlacklistedResult} from "./BlacklistedResult";
+import {SearchResult} from "./SearchResult";
+import {Token} from "./Token";
+
 /**
  * A class that provides functions to resolve queries
  */
-export class QueryResolver {
+export class QueryResolver extends BaseResolver {
+
+    /**
+     * Gets a user by id or handle
+     * @param userId
+     * @param handle
+     */
+    public async getUser({userId, handle}: {userId?: number, handle?: string}): Promise<User> {
+        let user: User;
+        if (userId) {
+            user = await User.findByPk(userId);
+        } else if (handle) {
+            user = await User.findOne({where: {handle}});
+        } else {
+            throw new GraphQLError("No handle or userId provided");
+        }
+        if (user) {
+            return user;
+        } else {
+            throw new UserNotFoundError(userId ?? handle);
+        }
+    }
+
+    /**
+     * Returns the instance of the currently logged in user
+     * @param args
+     * @param request
+     */
+    public async getSelf(args: null, request: any): Promise<User>  {
+        this.ensureLoggedIn(request);
+        return User.findByPk(request.session.userId);
+    }
+
+    /**
+     * Returns a post for a given post id.
+     * @param postId
+     */
+    public async getPost({postId}: {postId: number}): Promise<Post> {
+        const post = await Post.findByPk(postId);
+        if (post) {
+            return post;
+        } else {
+            throw new PostNotFoundGqlError(postId);
+        }
+    }
+
+    /**
+     * Returns a chat for a given chat id
+     * @param chatId
+     */
+    public async getChat({chatId}: {chatId: number}): Promise<ChatRoom> {
+        const chat = await ChatRoom.findByPk(chatId);
+        if (chat) {
+            return chat;
+        } else {
+            throw new ChatNotFoundError(chatId);
+        }
+    }
+
+    /**
+     * Returns a group for a given group id.
+     * @param groupId
+     */
+    public async getGroup({groupId}: {groupId: number}): Promise<Group> {
+        const group = await Group.findByPk(groupId);
+        if (group) {
+            return group;
+        } else {
+            throw new GroupNotFoundError(groupId);
+        }
+    }
+
+    /**
+     * Returns the request for a given id.
+     * @param requestId
+     */
+    public async getRequest({requestId}: {requestId: number}): Promise<Request> {
+        const request = await Request.findByPk(requestId);
+        if (request) {
+            return request;
+        } else {
+            throw new RequestNotFoundError(requestId);
+        }
+    }
+
+    /**
+     * Searches for posts, groups, users, events and returns a search result.
+     * @param query
+     * @param first
+     * @param offset
+     */
+    public async search({query, first, offset}: {query: number, first: number, offset: number}): Promise<SearchResult> {
+        const limit = first;
+        const users = await User.findAll({
+            limit,
+            offset,
+            where: {
+                [Op.or]: [
+                    {handle: {[Op.iRegexp]: query}},
+                    {username: {[Op.iRegexp]: query}},
+                ],
+            },
+        });
+        const groups = await Group.findAll({
+            limit,
+            offset,
+            where: {name: {[Op.iRegexp]: query}},
+        });
+        const posts = await Post.findAll({
+            limit,
+            offset,
+            where: {content: {[Op.iRegexp]: query}},
+        });
+        const events = await Event.findAll({
+            limit,
+            offset,
+            where: {name: {[Op.iRegexp]: query}},
+        });
+        return new SearchResult(users, groups, posts, events);
+    }
+
+    /**
+     * Returns the posts with a specific sorting
+     * @param first
+     * @param offset
+     * @param sort
+     */
+    public async getPosts({first, offset, sort}: {first: number, offset: number, sort: dataaccess.SortType}):
+        Promise<Post[]> {
+        return await dataaccess.getPosts(first, offset, sort);
+    }
+
+    /**
+     * Returns all activities
+     */
+    public async getActivities(): Promise<Activity[]> {
+        return  Activity.findAll();
+    }
+
+    /**
+     * Returns the token for a user by login
+     * @param email
+     * @param passwordHash
+     */
+    public async getToken({email, passwordHash}: {email: string, passwordHash: string}): Promise<Token> {
+        const user = await dataaccess.getUserByLogin(email, passwordHash);
+        return new Token(await user.token(), Number(user.authExpire).toString());
+    }
+
+    /**
+     * Returns if a input phrase contains blacklisted phrases and which one
+     * @param phrase
+     */
+    public async blacklisted({phrase}: {phrase: string}): Promise<BlacklistedResult> {
+        const phrases = await dataaccess.checkBlacklisted(phrase);
+        return new BlacklistedResult(phrases.length > 0, phrases
+            .map((p) => p.phrase));
+    }
+
+    /**
+     * Returns all blacklisted phrases with pagination
+     * @param first
+     * @param offset
+     */
+    public async getBlacklistedPhrases({first, offset}: {first: number, offset: number}): Promise<string[]> {
+        return (await BlacklistedPhrase.findAll({limit: first, offset}))
+            .map((p) => p.phrase);
+    }
 }
diff --git a/src/graphql/SearchResult.ts b/src/graphql/SearchResult.ts
new file mode 100644
index 0000000..739f023
--- /dev/null
+++ b/src/graphql/SearchResult.ts
@@ -0,0 +1,13 @@
+import {Group, Post, User, Event} from "../lib/models";
+
+/**
+ * A class to wrap search results returned by the search resolver
+ */
+export class SearchResult {
+    constructor(
+        public users: User[],
+        public groups: Group[],
+        public posts: Post[],
+        public events: Event[],
+    ) {}
+}
diff --git a/src/graphql/Token.ts b/src/graphql/Token.ts
new file mode 100644
index 0000000..f56d369
--- /dev/null
+++ b/src/graphql/Token.ts
@@ -0,0 +1,9 @@
+/**
+ * A class representing a token that can be used with bearer authentication
+ */
+export class Token {
+    constructor(
+        public value: string,
+        public expires: string,
+    ) {}
+}
diff --git a/src/lib/dataAccess.ts b/src/lib/dataAccess.ts
index 11b7d46..8fc11c9 100644
--- a/src/lib/dataAccess.ts
+++ b/src/lib/dataAccess.ts
@@ -205,7 +205,7 @@ namespace dataaccess {
      * Deletes a post
      * @param postId
      */
-    export async function deletePost(postId: number): Promise<boolean | GraphQLError> {
+    export async function deletePost(postId: number): Promise<boolean> {
         try {
             const post = await models.Post.findByPk(postId, {include: [{model: Activity}, {association: "rAuthor"}]});
             const activity = await post.activity();
diff --git a/src/lib/errors/InvalidEmailError.ts b/src/lib/errors/InvalidEmailError.ts
new file mode 100644
index 0000000..ea97b66
--- /dev/null
+++ b/src/lib/errors/InvalidEmailError.ts
@@ -0,0 +1,10 @@
+import {BaseError} from "./BaseError";
+
+/**
+ * An error that is thrown when a user tries to register with an invalid email
+ */
+export class InvalidEmailError extends BaseError {
+    constructor(email: string) {
+        super(`'${email}' is not a valid email address!`);
+    }
+}
diff --git a/src/lib/errors/NotAGroupAdminError.ts b/src/lib/errors/NotAGroupAdminError.ts
new file mode 100644
index 0000000..2538c37
--- /dev/null
+++ b/src/lib/errors/NotAGroupAdminError.ts
@@ -0,0 +1,14 @@
+import * as status from "http-status";
+import {BaseError} from "./BaseError";
+
+/**
+ * An error that is thrown when a non-admin tries to perform an admin action
+ */
+export class NotAGroupAdminError extends BaseError {
+    public readonly statusCode = status.FORBIDDEN;
+
+    constructor(groupId: number) {
+        super(`You are not an admin of '${groupId}'`);
+    }
+
+}
diff --git a/src/lib/errors/NotAnAdminError.ts b/src/lib/errors/NotAnAdminError.ts
new file mode 100644
index 0000000..b9454d0
--- /dev/null
+++ b/src/lib/errors/NotAnAdminError.ts
@@ -0,0 +1,13 @@
+import {BaseError} from "./BaseError";
+
+/**
+ * An error that is thrown when a non admin tries to perform an admin action
+ */
+export class NotAnAdminError extends BaseError {
+
+    public readonly statusCode = httpStatus.FORBIDDEN;
+
+    constructor() {
+        super("You are not a site admin!");
+    }
+}
diff --git a/src/lib/errors/NotTheGroupCreatorError.ts b/src/lib/errors/NotTheGroupCreatorError.ts
new file mode 100644
index 0000000..7b1e748
--- /dev/null
+++ b/src/lib/errors/NotTheGroupCreatorError.ts
@@ -0,0 +1,14 @@
+import * as status from "http-status";
+import {BaseError} from "./BaseError";
+
+/**
+ * An error that is thrown when a non-admin tries to perform an admin action
+ */
+export class NotTheGroupCreatorError extends BaseError {
+    public readonly statusCode = status.FORBIDDEN;
+
+    constructor(groupId: number) {
+        super(`You are not the creator of '${groupId}'`);
+    }
+
+}
diff --git a/src/lib/errors/PostNotFoundError.ts b/src/lib/errors/PostNotFoundError.ts
new file mode 100644
index 0000000..76fcf77
--- /dev/null
+++ b/src/lib/errors/PostNotFoundError.ts
@@ -0,0 +1,10 @@
+import {BaseError} from "./BaseError";
+
+/**
+ * An error that is thrown when a post was not found
+ */
+export class PostNotFoundError extends BaseError {
+    constructor(postId: number) {
+        super(`Post '${postId}' not found!`);
+    }
+}
diff --git a/src/lib/errors/RequestNotFoundError.ts b/src/lib/errors/RequestNotFoundError.ts
index cd94fc5..46fa064 100644
--- a/src/lib/errors/RequestNotFoundError.ts
+++ b/src/lib/errors/RequestNotFoundError.ts
@@ -5,7 +5,11 @@ import {BaseError} from "./BaseError";
  * An error that is thrown when a request for a sender, receiver and type was not found
  */
 export class RequestNotFoundError extends BaseError {
-    constructor(sender: number, receiver: number, type: dataaccess.RequestType) {
-        super(`Request with sender '${sender}' and receiver '${receiver}' of type '${type}' not found.`);
+    constructor(sender: number, receiver?: number, type?: dataaccess.RequestType) {
+        if (!receiver) {
+            super(`Request with id '${sender} not found.'`);
+        } else {
+            super(`Request with sender '${sender}' and receiver '${receiver}' of type '${type}' not found.`);
+        }
     }
 }