diff --git a/config.json.example b/config.json.example
index 306e1bb24e..3f6ba7769e 100644
--- a/config.json.example
+++ b/config.json.example
@@ -74,5 +74,6 @@
   "TRANSIFEX_SLACK_CHANNEL": "transifex",
   "WEB_CONCURRENCY": 1,
   "SKIP_SSL_CHECK_KEY": "key",
-  "ENABLE_STACKDRIVER_TRACING": "false"
+  "ENABLE_STACKDRIVER_TRACING": "false",
+  "BLOCKED_IPS": ""
 }
diff --git a/test/api/unit/libs/errors.test.js b/test/api/unit/libs/errors.test.js
index 4de2e4499f..5662fa3ced 100644
--- a/test/api/unit/libs/errors.test.js
+++ b/test/api/unit/libs/errors.test.js
@@ -3,6 +3,7 @@ import {
   CustomError,
   NotAuthorized,
   BadRequest,
+  Forbidden,
   InternalServerError,
   NotFound,
   NotificationNotFound,
@@ -113,6 +114,32 @@ describe('Custom Errors', () => {
     });
   });
 
+  describe('Forbidden', () => {
+    it('is an instance of CustomError', () => {
+      const forbiddenError = new Forbidden();
+
+      expect(forbiddenError).to.be.an.instanceOf(CustomError);
+    });
+
+    it('it returns an http code of 401', () => {
+      const forbiddenError = new Forbidden();
+
+      expect(forbiddenError.httpCode).to.eql(403);
+    });
+
+    it('returns a default message', () => {
+      const forbiddenError = new Forbidden();
+
+      expect(forbiddenError.message).to.eql('Access forbidden.');
+    });
+
+    it('allows a custom message', () => {
+      const forbiddenError = new Forbidden('Custom Error Message');
+
+      expect(forbiddenError.message).to.eql('Custom Error Message');
+    });
+  });
+
   describe('InternalServerError', () => {
     it('is an instance of CustomError', () => {
       const internalServerError = new InternalServerError();
diff --git a/test/api/unit/middlewares/ipBlocker.test.js b/test/api/unit/middlewares/ipBlocker.test.js
new file mode 100644
index 0000000000..c55534e4fe
--- /dev/null
+++ b/test/api/unit/middlewares/ipBlocker.test.js
@@ -0,0 +1,94 @@
+import nconf from 'nconf';
+import requireAgain from 'require-again';
+import {
+  generateRes,
+  generateReq,
+  generateNext,
+} from '../../../helpers/api-unit.helper';
+import { Forbidden } from '../../../../website/server/libs/errors';
+import apiError from '../../../../website/server/libs/apiError';
+
+function checkErrorThrown (next) {
+  expect(next).to.have.been.calledOnce;
+  const calledWith = next.getCall(0).args;
+  expect(calledWith[0].message).to.equal(apiError('ipAddressBlocked'));
+  expect(calledWith[0] instanceof Forbidden).to.equal(true);
+}
+
+function checkErrorNotThrown (next) {
+  expect(next).to.have.been.calledOnce;
+  const calledWith = next.getCall(0).args;
+  expect(typeof calledWith[0] === 'undefined').to.equal(true);
+}
+
+describe('ipBlocker middleware', () => {
+  const pathToIpBlocker = '../../../../website/server/middlewares/ipBlocker';
+
+  let res; let req; let next;
+
+  beforeEach(() => {
+    res = generateRes();
+    req = generateReq();
+    next = generateNext();
+  });
+
+  it('is disabled when the env var is not defined', () => {
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns(undefined);
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorNotThrown(next);
+  });
+
+  it('is disabled when the env var is an empty string', () => {
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns('');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorNotThrown(next);
+  });
+
+  it('is disabled when the env var contains comma separated empty strings', () => {
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns(' , , ');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorNotThrown(next);
+  });
+
+  it('does not throw when the ip does not match', () => {
+    req.headers['x-forwarded-for'] = '192.168.1.1';
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns('192.168.1.2');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorNotThrown(next);
+  });
+
+  it('throws when a matching ip exist in x-forwarded-for', () => {
+    req.headers['x-forwarded-for'] = '192.168.1.1';
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns('192.168.1.1');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorThrown(next);
+  });
+
+  it('trims ips in x-forwarded-for', () => {
+    req.headers['x-forwarded-for'] = '192.168.1.1';
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns(',  192.168.1.1 ,   192.168.1.4, ');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorThrown(next);
+  });
+
+  it('works when multiple ips are passed in x-forwarded-for', () => {
+    req.headers['x-forwarded-for'] = '192.168.1.4';
+    sandbox.stub(nconf, 'get').withArgs('BLOCKED_IPS').returns('192.168.1.1, 192.168.1.4, 192.168.1.3');
+    const attachIpBlocker = requireAgain(pathToIpBlocker).default;
+    attachIpBlocker(req, res, next);
+
+    checkErrorThrown(next);
+  });
+});
diff --git a/website/common/script/errors/apiErrorMessages.js b/website/common/script/errors/apiErrorMessages.js
index 1a99ec1d2e..e8a3edce8c 100644
--- a/website/common/script/errors/apiErrorMessages.js
+++ b/website/common/script/errors/apiErrorMessages.js
@@ -25,4 +25,6 @@ export default {
   missingCustomerId: 'Missing "req.query.customerId"',
   missingPaypalBlock: 'Missing "req.session.paypalBlock"',
   missingSubKey: 'Missing "req.query.sub"',
+
+  ipAddressBlocked: 'This IP address has been blocked from accessing Habitica. This may be due to a breach of our Terms of Service or technical issue originating at this IP address. For details or to ask to be unblocked, please email admin@habitica.com or ask your parent or guardian to email them. Include your Habitica @ Username or User Id in the email if you have one.',
 };
diff --git a/website/common/script/libs/errors.js b/website/common/script/libs/errors.js
index acdbe237d2..00d917d16b 100644
--- a/website/common/script/libs/errors.js
+++ b/website/common/script/libs/errors.js
@@ -42,6 +42,15 @@ export class NotFound extends CustomError {
   }
 }
 
+export class Forbidden extends CustomError {
+  constructor (customMessage) {
+    super();
+    this.name = this.constructor.name;
+    this.httpCode = 403;
+    this.message = customMessage || 'Access forbidden.';
+  }
+}
+
 export class NotImplementedError extends CustomError {
   constructor (str) {
     super();
diff --git a/website/server/libs/errors.js b/website/server/libs/errors.js
index 193e95f349..f0d505fb65 100644
--- a/website/server/libs/errors.js
+++ b/website/server/libs/errors.js
@@ -41,6 +41,19 @@ export const { BadRequest } = common.errors;
  */
 export const { NotFound } = common.errors;
 
+/**
+ * @apiDefine Forbidden
+ * @apiError Forbidden The requested resource was not found.
+ *
+ * @apiErrorExample Error-Response:
+ *     HTTP/1.1 403 Forbidden
+ *     {
+ *       "error": "Forbidden",
+ *       "message": "Access forbidden."
+ *     }
+ */
+export const { Forbidden } = common.errors;
+
 
 /**
  * @apiDefine NotificationNotFound
diff --git a/website/server/middlewares/index.js b/website/server/middlewares/index.js
index 580cf3a73b..e392dda8b5 100644
--- a/website/server/middlewares/index.js
+++ b/website/server/middlewares/index.js
@@ -21,6 +21,7 @@ import {
   forceSSL,
   forceHabitica,
 } from './redirects';
+import ipBlocker from './ipBlocker';
 import v1 from './v1';
 import v2 from './v2';
 import appRoutes from './appRoutes';
@@ -45,7 +46,8 @@ export default function attachMiddlewares (app, server) {
 
   if (!IS_PROD && !DISABLE_LOGGING) app.use(morgan('dev'));
 
-  app.use(helmet()); // See https://helmetjs.github.io/ for the list of headers enabled by default
+  // See https://helmetjs.github.io/ for the list of headers enabled by default
+  app.use(helmet());
 
   // add res.respond and res.t
   app.use(responseHandler);
@@ -56,6 +58,8 @@ export default function attachMiddlewares (app, server) {
 
   app.use(maintenanceMode);
 
+  app.use(ipBlocker);
+
   app.use(cors);
   app.use(forceSSL);
   app.use(forceHabitica);
diff --git a/website/server/middlewares/ipBlocker.js b/website/server/middlewares/ipBlocker.js
new file mode 100644
index 0000000000..69c2a48c1a
--- /dev/null
+++ b/website/server/middlewares/ipBlocker.js
@@ -0,0 +1,60 @@
+import nconf from 'nconf';
+import {
+  Forbidden,
+} from '../libs/errors';
+import apiError from '../libs/apiError';
+
+// Middleware to block unwanted IP addresses
+
+// NOTE: it's meant to be used behind a proxy (for example a load balancer)
+// that uses the 'x-forwarded-for' header to forward the original IP addresses.
+
+// A list of comma separated IPs to block
+// It works fine as long as the list is short,
+// if the list becomes too long for an env variable we'll switch to Redis.
+const BLOCKED_IPS_RAW = nconf.get('BLOCKED_IPS');
+
+const blockedIps = BLOCKED_IPS_RAW
+  ? BLOCKED_IPS_RAW
+    .trim()
+    .split(',')
+    .map(blockedIp => blockedIp.trim())
+    .filter(blockedIp => Boolean(blockedIp))
+  : [];
+
+export default function ipBlocker (req, res, next) {
+  // If there are no IPs to block, skip the middleware
+  if (blockedIps.length === 0) return next();
+
+  // If x-forwarded-for is undefined we're not behind the production proxy
+  const originIpsRaw = req.header('x-forwarded-for');
+  if (!originIpsRaw) return next();
+
+  // Format xxx.xxx.xxx.xxx, xxx.xxx.xxx.xxx (comma separated list of ip)
+  const originIps = originIpsRaw
+    .split(',')
+    .map(originIp => originIp.trim());
+
+  // We try to match any of the origins IPs against the blocked IPs list.
+  //
+  // In case we're behind a Google Cloud Load Balancer the last ip
+  // in the list is added by the load balancer.
+  // See https://cloud.google.com/load-balancing/docs/https#target-proxies
+  // In particular:
+  // << A Google Cloud external HTTP(S) load balancer adds two IP addresses to the header:
+  // the IP address of the requesting client and the external IP address of the load balancer's
+  // forwarding rule, in that order.
+  // Therefore, the IP address that immediately precedes the Google Cloud load balancer's
+  // IP address is the IP address of the system that contacts the load balancer.
+  // The system might be a client, or it might be another proxy server, outside Google Cloud,
+  // that forwards requests on behalf of a client. >>
+
+  const match = originIps.find(originIp => blockedIps.includes(originIp)) !== undefined;
+
+  if (match === true) {
+    // Not translated because no user is loaded at this point
+    return next(new Forbidden(apiError('ipAddressBlocked')));
+  }
+
+  return next();
+}