How do I get the client IP of a Tornado request?

mykhal's answer is right, however sometimes your application will be behind a proxy, for example if you use nginx and UWSGI and you will always get something like 127.0.0.1 for the remote IP. In this case you need to check the headers too, like:

remote_ip = self.request.headers.get("X-Real-IP") or \
            self.request.headers.get("X-Forwarded-For") or \
            self.request.remote_ip

Edit Oct 17th, 2019: include the commonly used header X-Forwarded-For which is used by AWS load balancers amongst others.

RequestHandler.request.remote_ip (from RequestHandler's instance)

you can inspect the response like:

...
class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write(repr(self.request))
...