diff --git a/common/locales/en/api-v3.json b/common/locales/en/api-v3.json
index ec2be7a366..019081bf35 100644
--- a/common/locales/en/api-v3.json
+++ b/common/locales/en/api-v3.json
@@ -75,6 +75,7 @@
   "questLevelTooHigh": "You must be Level <%= level %> to begin this quest.",
   "questAlreadyUnderway": "Your party is already on a quest. Try again when the current quest has ended.",
   "questAlreadyAccepted": "You already accepted the quest invitation.",
+  "questAlreadyRejected": "You already rejected the quest invitation.",
   "cantCancelActiveQuest": "You can not cancel an active quest, use the abort functionality.",
   "onlyLeaderCancelQuest": "Only the group or quest leader can cancel the quest.",
   "questInvitationDoesNotExist": "No quest invitation has been sent out yet."
diff --git a/common/locales/en/quests.json b/common/locales/en/quests.json
index 7b3fe7af43..5edae258e5 100644
--- a/common/locales/en/quests.json
+++ b/common/locales/en/quests.json
@@ -78,5 +78,6 @@
     "whichQuestStart": "Which quest do you want to start?",
     "getMoreQuests": "Get more quests",
     "unlockedAQuest": "You unlocked a quest!",
-    "leveledUpReceivedQuest": "You leveled up to <strong>Level <%= level %></strong> and received a quest scroll!"
+    "leveledUpReceivedQuest": "You leveled up to <strong>Level <%= level %></strong> and received a quest scroll!",
+    "questInvitationDoesNotExist": "No quest invitation has been sent out yet."
 }
diff --git a/test/api/v3/integration/quests/POST-groups_groupid_quests_reject.test.js b/test/api/v3/integration/quests/POST-groups_groupid_quests_reject.test.js
new file mode 100644
index 0000000000..1eb62aa0c6
--- /dev/null
+++ b/test/api/v3/integration/quests/POST-groups_groupid_quests_reject.test.js
@@ -0,0 +1,146 @@
+import {
+  createAndPopulateGroup,
+  translate as t,
+  generateUser,
+} from '../../../../helpers/api-v3-integration.helper';
+import { v4 as generateUUID } from 'uuid';
+
+describe('POST /groups/:groupId/quests/reject', () => {
+  let questingGroup;
+  let partyMembers;
+  let user;
+  let leader;
+
+  const PET_QUEST = 'whale';
+
+  beforeEach(async () => {
+    let { group, groupLeader, members } = await createAndPopulateGroup({
+      groupDetails: { type: 'party', privacy: 'private' },
+      members: 2,
+    });
+
+    questingGroup = group;
+    leader = groupLeader;
+    partyMembers = members;
+
+    await leader.update({
+      [`items.quests.${PET_QUEST}`]: 1,
+    });
+    user = await generateUser();
+  });
+
+  context('failure conditions', () => {
+    it('returns an error when group is not found', async () => {
+      await expect(partyMembers[0].post(`/groups/${generateUUID()}/quests/reject`))
+        .to.eventually.be.rejected.and.eql({
+          code: 404,
+          error: 'NotFound',
+          message: t('groupNotFound'),
+        });
+    });
+
+    it('does not accept quest for a group in which user is not a member', async () => {
+      await expect(user.post(`/groups/${questingGroup._id}/quests/accept`))
+      .to.eventually.be.rejected.and.eql({
+        code: 404,
+        error: 'NotFound',
+        message: t('groupNotFound'),
+      });
+    });
+
+    it('returns an error when group is a guild', async () => {
+      let { group: guild, groupLeader: guildLeader } = await createAndPopulateGroup({
+        groupDetails: { type: 'guild', privacy: 'private' },
+      });
+
+      await expect(guildLeader.post(`/groups/${guild._id}/quests/reject`))
+      .to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('guildQuestsNotSupported'),
+      });
+    });
+
+    it('returns an error when group is not on a quest', async () => {
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`))
+        .to.eventually.be.rejected.and.eql({
+          code: 404,
+          error: 'NotFound',
+          message: t('questInvitationDoesNotExist'),
+        });
+    });
+
+    it('return an error when an user rejects an invite twice', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`);
+
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`))
+      .to.eventually.be.rejected.and.eql({
+        code: 400,
+        error: 'BadRequest',
+        message: t('questAlreadyRejected'),
+      });
+    });
+
+    it('return an error when an user rejects an invite already accepted', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`))
+      .to.eventually.be.rejected.and.eql({
+        code: 400,
+        error: 'BadRequest',
+        message: t('questAlreadyAccepted'),
+      });
+    });
+
+    it('does not reject invite for a quest already underway', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+      // quest will start after everyone has accepted
+      await partyMembers[1].post(`/groups/${questingGroup._id}/quests/accept`);
+
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`))
+      .to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('questAlreadyUnderway'),
+      });
+    });
+  });
+
+  context('successfully quest rejection', () => {
+    let cleanUserQuestObj = {
+      key: null,
+      progress: {
+        up: 0,
+        down: 0,
+        collect: {},
+      },
+      completed: null,
+      RSVPNeeded: false,
+    };
+
+    it('rejects a quest invitation', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+
+      let res = await partyMembers[0].post(`/groups/${questingGroup._id}/quests/reject`);
+      await partyMembers[0].sync();
+      await questingGroup.sync();
+
+      expect(partyMembers[0].party.quest).to.eql(cleanUserQuestObj);
+      expect(questingGroup.quest.members[partyMembers[0]._id]).to.be.false;
+      expect(questingGroup.quest.active).to.be.false;
+      expect(res).to.eql(questingGroup.quest);
+    });
+
+    it('starts the quest when the last user reject', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+      await partyMembers[1].post(`/groups/${questingGroup._id}/quests/reject`);
+      await questingGroup.sync();
+
+      expect(questingGroup.quest.active).to.be.true;
+    });
+  });
+});
diff --git a/website/src/controllers/api-v3/quests.js b/website/src/controllers/api-v3/quests.js
index fc1555f54d..e85ea860ce 100644
--- a/website/src/controllers/api-v3/quests.js
+++ b/website/src/controllers/api-v3/quests.js
@@ -23,7 +23,7 @@ import { quests as questScrolls } from '../../../../common/script/content';
 function canStartQuestAutomatically (group)  {
   // If all members are either true (accepted) or false (rejected) return true
   // If any member is null/undefined (undecided) return false
-  return _.every(group.quest.members, Boolean);
+  return _.every(group.quest.members, _.isBoolean);
 }
 
 let api = {};
@@ -182,6 +182,64 @@ api.acceptQuest = {
   },
 };
 
+/**
+ * @api {post} /groups/:groupId/quests/reject Reject a quest
+ * @apiVersion 3.0.0
+ * @apiName RejectQuest
+ * @apiGroup Group
+ *
+ * @apiParam {string} groupId The group _id (or 'party')
+ *
+ * @apiSuccess {Object} quest Quest Object
+ */
+api.rejectQuest = {
+  method: 'POST',
+  url: '/groups/:groupId/quests/reject',
+  middlewares: [authWithHeaders(), cron],
+  async handler (req, res) {
+    let user = res.locals.user;
+
+    req.checkParams('groupId', res.t('groupIdRequired')).notEmpty();
+
+    let validationErrors = req.validationErrors();
+    if (validationErrors) throw validationErrors;
+
+    let group = await Group.getGroup({user, groupId: req.params.groupId, fields: 'type quest'});
+    if (!group) throw new NotFound(res.t('groupNotFound'));
+    if (group.type !== 'party') throw new NotAuthorized(res.t('guildQuestsNotSupported'));
+    if (!group.quest.key) throw new NotFound(res.t('questInvitationDoesNotExist'));
+    if (group.quest.active) throw new NotAuthorized(res.t('questAlreadyUnderway'));
+    if (group.quest.members[user._id]) throw new BadRequest(res.t('questAlreadyAccepted'));
+    if (group.quest.members[user._id] === false) throw new BadRequest(res.t('questAlreadyRejected'));
+
+    group.quest.members[user._id] = false;
+    group.markModified('quest.members');
+
+    user.party.quest = Group.cleanQuestProgress();
+    user.markModified('party.quest');
+
+    if (canStartQuestAutomatically(group)) {
+      await group.startQuest(user);
+    }
+
+    let [savedGroup] = await Q.all([
+      group.save(),
+      user.save(),
+    ]);
+
+    res.respond(200, savedGroup.quest);
+
+    analytics.track('quest', {
+      category: 'behavior',
+      owner: false,
+      response: 'reject',
+      gaLabel: 'reject',
+      questName: group.quest.key,
+      uuid: user._id,
+    });
+  },
+};
+
 /**
  * @api {post} /groups/:groupId/quests/cancel Cancels a quest
  * @apiVersion 3.0.0
@@ -229,5 +287,4 @@ api.cancelQuest = {
   },
 };
 
-
 export default api;
diff --git a/website/src/models/group.js b/website/src/models/group.js
index 1af2c8f7b5..d955ed1fda 100644
--- a/website/src/models/group.js
+++ b/website/src/models/group.js
@@ -302,7 +302,6 @@ schema.methods.startQuest = async function startQuest (user) {
 
 // return a clean object for user.quest
 function _cleanQuestProgress (merge) {
-  // TODO clone? (also in sendChat message)
   let clean = {
     key: null,
     progress: {