diff --git a/app/controllers/api/v1/reports_controller.rb b/app/controllers/api/v1/reports_controller.rb
index 22828217d2..f5095e0730 100644
--- a/app/controllers/api/v1/reports_controller.rb
+++ b/app/controllers/api/v1/reports_controller.rb
@@ -13,14 +13,14 @@ class Api::V1::ReportsController < Api::BaseController
   end
 
   def create
-    @report = current_account.reports.create!(
-      target_account: reported_account,
+    @report = ReportService.new.call(
+      current_account,
+      reported_account,
       status_ids: reported_status_ids,
-      comment: report_params[:comment]
+      comment: report_params[:comment],
+      forward: report_params[:forward]
     )
 
-    User.staff.includes(:account).each { |u| AdminMailer.new_report(u.account, @report).deliver_later }
-
     render json: @report, serializer: REST::ReportSerializer
   end
 
@@ -39,6 +39,6 @@ class Api::V1::ReportsController < Api::BaseController
   end
 
   def report_params
-    params.permit(:account_id, :comment, status_ids: [])
+    params.permit(:account_id, :comment, :forward, status_ids: [])
   end
 end
diff --git a/app/javascript/mastodon/actions/reports.js b/app/javascript/mastodon/actions/reports.js
index b19a07285b..afa0c34121 100644
--- a/app/javascript/mastodon/actions/reports.js
+++ b/app/javascript/mastodon/actions/reports.js
@@ -10,6 +10,7 @@ export const REPORT_SUBMIT_FAIL    = 'REPORT_SUBMIT_FAIL';
 
 export const REPORT_STATUS_TOGGLE  = 'REPORT_STATUS_TOGGLE';
 export const REPORT_COMMENT_CHANGE = 'REPORT_COMMENT_CHANGE';
+export const REPORT_FORWARD_CHANGE = 'REPORT_FORWARD_CHANGE';
 
 export function initReport(account, status) {
   return dispatch => {
@@ -45,6 +46,7 @@ export function submitReport() {
       account_id: getState().getIn(['reports', 'new', 'account_id']),
       status_ids: getState().getIn(['reports', 'new', 'status_ids']),
       comment: getState().getIn(['reports', 'new', 'comment']),
+      forward: getState().getIn(['reports', 'new', 'forward']),
     }).then(response => {
       dispatch(closeModal());
       dispatch(submitReportSuccess(response.data));
@@ -78,3 +80,10 @@ export function changeReportComment(comment) {
     comment,
   };
 };
+
+export function changeReportForward(forward) {
+  return {
+    type: REPORT_FORWARD_CHANGE,
+    forward,
+  };
+};
diff --git a/app/javascript/mastodon/features/ui/components/report_modal.js b/app/javascript/mastodon/features/ui/components/report_modal.js
index b5dfa422e4..3a7e4df762 100644
--- a/app/javascript/mastodon/features/ui/components/report_modal.js
+++ b/app/javascript/mastodon/features/ui/components/report_modal.js
@@ -1,6 +1,6 @@
 import React from 'react';
 import { connect } from 'react-redux';
-import { changeReportComment, submitReport } from '../../../actions/reports';
+import { changeReportComment, changeReportForward, submitReport } from '../../../actions/reports';
 import { refreshAccountTimeline } from '../../../actions/timelines';
 import PropTypes from 'prop-types';
 import ImmutablePropTypes from 'react-immutable-proptypes';
@@ -10,6 +10,7 @@ import StatusCheckBox from '../../report/containers/status_check_box_container';
 import { OrderedSet } from 'immutable';
 import ImmutablePureComponent from 'react-immutable-pure-component';
 import Button from '../../../components/button';
+import Toggle from 'react-toggle';
 
 const messages = defineMessages({
   placeholder: { id: 'report.placeholder', defaultMessage: 'Additional comments' },
@@ -26,6 +27,7 @@ const makeMapStateToProps = () => {
       isSubmitting: state.getIn(['reports', 'new', 'isSubmitting']),
       account: getAccount(state, accountId),
       comment: state.getIn(['reports', 'new', 'comment']),
+      forward: state.getIn(['reports', 'new', 'forward']),
       statusIds: OrderedSet(state.getIn(['timelines', `account:${accountId}`, 'items'])).union(state.getIn(['reports', 'new', 'status_ids'])),
     };
   };
@@ -42,14 +44,19 @@ export default class ReportModal extends ImmutablePureComponent {
     account: ImmutablePropTypes.map,
     statusIds: ImmutablePropTypes.orderedSet.isRequired,
     comment: PropTypes.string.isRequired,
+    forward: PropTypes.bool,
     dispatch: PropTypes.func.isRequired,
     intl: PropTypes.object.isRequired,
   };
 
-  handleCommentChange = (e) => {
+  handleCommentChange = e => {
     this.props.dispatch(changeReportComment(e.target.value));
   }
 
+  handleForwardChange = e => {
+    this.props.dispatch(changeReportForward(e.target.checked));
+  }
+
   handleSubmit = () => {
     this.props.dispatch(submitReport());
   }
@@ -65,12 +72,14 @@ export default class ReportModal extends ImmutablePureComponent {
   }
 
   render () {
-    const { account, comment, intl, statusIds, isSubmitting } = this.props;
+    const { account, comment, intl, statusIds, isSubmitting, forward } = this.props;
 
     if (!account) {
       return null;
     }
 
+    const domain = account.get('acct').split('@')[1];
+
     return (
       <div className='modal-root__modal report-modal'>
         <div className='report-modal__target'>
@@ -78,13 +87,9 @@ export default class ReportModal extends ImmutablePureComponent {
         </div>
 
         <div className='report-modal__container'>
-          <div className='report-modal__statuses'>
-            <div>
-              {statusIds.map(statusId => <StatusCheckBox id={statusId} key={statusId} disabled={isSubmitting} />)}
-            </div>
-          </div>
-
           <div className='report-modal__comment'>
+            <p><FormattedMessage id='report.hint' defaultMessage='The report will be sent to your instance moderators. You can provide an explanation of why you are reporting this account below:' /></p>
+
             <textarea
               className='setting-text light'
               placeholder={intl.formatMessage(messages.placeholder)}
@@ -92,11 +97,26 @@ export default class ReportModal extends ImmutablePureComponent {
               onChange={this.handleCommentChange}
               disabled={isSubmitting}
             />
-          </div>
-        </div>
 
-        <div className='report-modal__action-bar'>
-          <Button disabled={isSubmitting} text={intl.formatMessage(messages.submit)} onClick={this.handleSubmit} />
+            {domain && (
+              <div>
+                <p><FormattedMessage id='report.forward_hint' defaultMessage='The account is from another server. Send an anonymized copy of the report there as well?' /></p>
+
+                <div className='setting-toggle'>
+                  <Toggle id='report-forward' checked={forward} disabled={isSubmitting} onChange={this.handleForwardChange} />
+                  <label htmlFor='report-forward' className='setting-toggle__label'><FormattedMessage id='report.forward' defaultMessage='Forward to {target}' values={{ target: domain }} /></label>
+                </div>
+              </div>
+            )}
+
+            <Button disabled={isSubmitting} text={intl.formatMessage(messages.submit)} onClick={this.handleSubmit} />
+          </div>
+
+          <div className='report-modal__statuses'>
+            <div>
+              {statusIds.map(statusId => <StatusCheckBox id={statusId} key={statusId} disabled={isSubmitting} />)}
+            </div>
+          </div>
         </div>
       </div>
     );
diff --git a/app/javascript/mastodon/reducers/reports.js b/app/javascript/mastodon/reducers/reports.js
index a08bbec387..21ae6f93f7 100644
--- a/app/javascript/mastodon/reducers/reports.js
+++ b/app/javascript/mastodon/reducers/reports.js
@@ -6,6 +6,7 @@ import {
   REPORT_CANCEL,
   REPORT_STATUS_TOGGLE,
   REPORT_COMMENT_CHANGE,
+  REPORT_FORWARD_CHANGE,
 } from '../actions/reports';
 import { Map as ImmutableMap, Set as ImmutableSet } from 'immutable';
 
@@ -15,6 +16,7 @@ const initialState = ImmutableMap({
     account_id: null,
     status_ids: ImmutableSet(),
     comment: '',
+    forward: false,
   }),
 });
 
@@ -42,6 +44,8 @@ export default function reports(state = initialState, action) {
     });
   case REPORT_COMMENT_CHANGE:
     return state.setIn(['new', 'comment'], action.comment);
+  case REPORT_FORWARD_CHANGE:
+    return state.setIn(['new', 'forward'], action.forward);
   case REPORT_SUBMIT_REQUEST:
     return state.setIn(['new', 'isSubmitting'], true);
   case REPORT_SUBMIT_FAIL:
diff --git a/app/javascript/styles/mastodon/components.scss b/app/javascript/styles/mastodon/components.scss
index 0224009ee1..213f4df47f 100644
--- a/app/javascript/styles/mastodon/components.scss
+++ b/app/javascript/styles/mastodon/components.scss
@@ -3891,8 +3891,7 @@ a.status-card {
 
 .boost-modal__action-bar,
 .confirmation-modal__action-bar,
-.mute-modal__action-bar,
-.report-modal__action-bar {
+.mute-modal__action-bar {
   display: flex;
   justify-content: space-between;
   background: $ui-secondary-color;
@@ -3936,21 +3935,94 @@ a.status-card {
   vertical-align: middle;
 }
 
+.report-modal {
+  width: 90vw;
+  max-width: 700px;
+}
+
+.report-modal__container {
+  display: flex;
+  border-top: 1px solid $ui-secondary-color;
+
+  @media screen and (max-width: 480px) {
+    flex-wrap: wrap;
+    overflow-y: auto;
+  }
+}
+
 .report-modal__statuses,
 .report-modal__comment {
-  padding: 10px;
+  box-sizing: border-box;
+  width: 50%;
+
+  @media screen and (max-width: 480px) {
+    width: 100%;
+  }
 }
 
 .report-modal__statuses {
+  flex: 1 1 auto;
   min-height: 20vh;
   max-height: 40vh;
   overflow-y: auto;
   overflow-x: hidden;
+
+  @media screen and (max-width: 480px) {
+    max-height: 10vh;
+  }
 }
 
 .report-modal__comment {
+  padding: 20px;
+  border-right: 1px solid $ui-secondary-color;
+  max-width: 320px;
+
+  p {
+    font-size: 14px;
+    line-height: 20px;
+    margin-bottom: 20px;
+  }
+
   .setting-text {
-    margin-top: 10px;
+    display: block;
+    box-sizing: border-box;
+    width: 100%;
+    margin: 0;
+    color: $ui-base-color;
+    background: $white;
+    padding: 10px;
+    font-family: inherit;
+    font-size: 14px;
+    resize: vertical;
+    border: 0;
+    outline: 0;
+    border-radius: 4px;
+    border: 1px solid $ui-secondary-color;
+    margin-bottom: 20px;
+
+    &:focus {
+      border: 1px solid darken($ui-secondary-color, 8%);
+    }
+  }
+
+  .setting-toggle {
+    margin-top: 20px;
+    margin-bottom: 24px;
+
+    &__label {
+      color: $ui-base-color;
+      font-size: 14px;
+    }
+  }
+
+  @media screen and (max-width: 480px) {
+    padding: 10px;
+    max-width: 100%;
+    order: 2;
+
+    .setting-toggle {
+      margin-bottom: 4px;
+    }
   }
 }
 
@@ -4043,6 +4115,10 @@ a.status-card {
   }
 }
 
+.report-modal__target {
+  padding: 20px;
+}
+
 .loading-bar {
   background-color: $ui-highlight-color;
   height: 3px;
diff --git a/app/lib/activitypub/activity.rb b/app/lib/activitypub/activity.rb
index 4617905c63..6f4a3b4911 100644
--- a/app/lib/activitypub/activity.rb
+++ b/app/lib/activitypub/activity.rb
@@ -44,6 +44,8 @@ class ActivityPub::Activity
         ActivityPub::Activity::Accept
       when 'Reject'
         ActivityPub::Activity::Reject
+      when 'Flag'
+        ActivityPub::Activity::Flag
       end
     end
   end
diff --git a/app/lib/activitypub/activity/flag.rb b/app/lib/activitypub/activity/flag.rb
new file mode 100644
index 0000000000..36d3c57300
--- /dev/null
+++ b/app/lib/activitypub/activity/flag.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class ActivityPub::Activity::Flag < ActivityPub::Activity
+  def perform
+    target_accounts            = object_uris.map { |uri| account_from_uri(uri) }.compact.select(&:local?)
+    target_statuses_by_account = object_uris.map { |uri| status_from_uri(uri) }.compact.select(&:local?).group_by(&:account_id)
+
+    target_accounts.each do |target_account|
+      next if Report.where(account: @account, target_account: target_account).exists?
+
+      target_statuses = target_statuses_by_account[target_account.id]
+
+      ReportService.new.call(
+        @account,
+        target_account,
+        status_ids: target_statuses.nil? ? [] : target_statuses.map(&:id),
+        comment: @json['content'] || ''
+      )
+    end
+  end
+
+  def object_uris
+    @object_uris ||= Array(@object.is_a?(Array) ? @object.map { |item| value_or_id(item) } : value_or_id(@object))
+  end
+end
diff --git a/app/models/report.rb b/app/models/report.rb
index f55fb6d3ee..dd123fc151 100644
--- a/app/models/report.rb
+++ b/app/models/report.rb
@@ -24,6 +24,10 @@ class Report < ApplicationRecord
 
   validates :comment, length: { maximum: 1000 }
 
+  def object_type
+    :flag
+  end
+
   def statuses
     Status.where(id: status_ids).includes(:account, :media_attachments, :mentions)
   end
diff --git a/app/serializers/activitypub/flag_serializer.rb b/app/serializers/activitypub/flag_serializer.rb
new file mode 100644
index 0000000000..53e8f726db
--- /dev/null
+++ b/app/serializers/activitypub/flag_serializer.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class ActivityPub::FlagSerializer < ActiveModel::Serializer
+  attributes :id, :type, :actor, :content
+  attribute :virtual_object, key: :object
+
+  def id
+    # This is nil for now
+    ActivityPub::TagManager.instance.uri_for(object)
+  end
+
+  def type
+    'Flag'
+  end
+
+  def actor
+    ActivityPub::TagManager.instance.uri_for(instance_options[:account] || object.account)
+  end
+
+  def virtual_object
+    [ActivityPub::TagManager.instance.uri_for(object.target_account)] + object.statuses.map { |s| ActivityPub::TagManager.instance.uri_for(s) }
+  end
+
+  def content
+    object.comment
+  end
+end
diff --git a/app/services/report_service.rb b/app/services/report_service.rb
new file mode 100644
index 0000000000..c06488a6de
--- /dev/null
+++ b/app/services/report_service.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+class ReportService < BaseService
+  def call(source_account, target_account, options = {})
+    @source_account = source_account
+    @target_account = target_account
+    @status_ids     = options.delete(:status_ids) || []
+    @comment        = options.delete(:comment) || ''
+    @options        = options
+
+    create_report!
+    notify_staff!
+    forward_to_origin! if !@target_account.local? && ActiveModel::Type::Boolean.new.cast(@options[:forward])
+
+    @report
+  end
+
+  private
+
+  def create_report!
+    @report = @source_account.reports.create!(
+      target_account: @target_account,
+      status_ids: @status_ids,
+      comment: @comment
+    )
+  end
+
+  def notify_staff!
+    User.staff.includes(:account).each do |u|
+      AdminMailer.new_report(u.account, @report).deliver_later
+    end
+  end
+
+  def forward_to_origin!
+    ActivityPub::DeliveryWorker.perform_async(
+      payload,
+      some_local_account.id,
+      @target_account.inbox_url
+    )
+  end
+
+  def payload
+    Oj.dump(ActiveModelSerializers::SerializableResource.new(
+      @report,
+      serializer: ActivityPub::FlagSerializer,
+      adapter: ActivityPub::Adapter,
+      account: some_local_account
+    ).as_json)
+  end
+
+  def some_local_account
+    @some_local_account ||= Account.local.where(suspended: false).first
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 213fbc8d9a..c6b81df34e 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -537,6 +537,7 @@ ActiveRecord::Schema.define(version: 20180211015820) do
   add_foreign_key "account_moderation_notes", "accounts", column: "target_account_id"
   add_foreign_key "accounts", "accounts", column: "moved_to_account_id", on_delete: :nullify
   add_foreign_key "admin_action_logs", "accounts", on_delete: :cascade
+  add_foreign_key "backups", "users", on_delete: :nullify
   add_foreign_key "blocks", "accounts", column: "target_account_id", name: "fk_9571bfabc1", on_delete: :cascade
   add_foreign_key "blocks", "accounts", name: "fk_4269e03e65", on_delete: :cascade
   add_foreign_key "conversation_mutes", "accounts", name: "fk_225b4212bb", on_delete: :cascade
diff --git a/spec/lib/activitypub/activity/flag_spec.rb b/spec/lib/activitypub/activity/flag_spec.rb
new file mode 100644
index 0000000000..3f082a8137
--- /dev/null
+++ b/spec/lib/activitypub/activity/flag_spec.rb
@@ -0,0 +1,37 @@
+require 'rails_helper'
+
+RSpec.describe ActivityPub::Activity::Flag do
+  let(:sender)  { Fabricate(:account, domain: 'example.com') }
+  let(:flagged) { Fabricate(:account) }
+  let(:status)  { Fabricate(:status, account: flagged, uri: 'foobar') }
+
+  let(:json) do
+    {
+      '@context': 'https://www.w3.org/ns/activitystreams',
+      id: nil,
+      type: 'Flag',
+      content: 'Boo!!',
+      actor: ActivityPub::TagManager.instance.uri_for(sender),
+      object: [
+        ActivityPub::TagManager.instance.uri_for(flagged),
+        ActivityPub::TagManager.instance.uri_for(status),
+      ],
+    }.with_indifferent_access
+  end
+
+  describe '#perform' do
+    subject { described_class.new(json, sender) }
+
+    before do
+      subject.perform
+    end
+
+    it 'creates a report' do
+      report = Report.find_by(account: sender, target_account: flagged)
+
+      expect(report).to_not be_nil
+      expect(report.comment).to eq 'Boo!!'
+      expect(report.status_ids).to eq [status.id]
+    end
+  end
+end
diff --git a/spec/services/report_service_spec.rb b/spec/services/report_service_spec.rb
new file mode 100644
index 0000000000..2f926ef00e
--- /dev/null
+++ b/spec/services/report_service_spec.rb
@@ -0,0 +1,25 @@
+require 'rails_helper'
+
+RSpec.describe ReportService do
+  subject { described_class.new }
+
+  let(:source_account) { Fabricate(:account) }
+
+  context 'for a remote account' do
+    let(:remote_account) { Fabricate(:account, domain: 'example.com', protocol: :activitypub, inbox_url: 'http://example.com/inbox') }
+
+    before do
+      stub_request(:post, 'http://example.com/inbox').to_return(status: 200)
+    end
+
+    it 'sends ActivityPub payload when forward is true' do
+      subject.call(source_account, remote_account, forward: true)
+      expect(a_request(:post, 'http://example.com/inbox')).to have_been_made
+    end
+
+    it 'does not send anything when forward is false' do
+      subject.call(source_account, remote_account, forward: false)
+      expect(a_request(:post, 'http://example.com/inbox')).to_not have_been_made
+    end
+  end
+end