I applied online. After one brief interview with a recruiter (there were simple technical questions that every iOS engineer should answer, pretty easily), I had two screening interviews with Yelp engineers.

There was 20-25 minutes talking about my background and projects I mentioned in my resume, and about 20 minutes coding some simple algorithmic question. After that, I was invited to an onsite interview in San Francisco.

There were four interviews with different engineers. I was really afraid of doing something wrong and thought it would be the longest hours of my life. But the time passed very quickly. Everyone was friendly and inspired. We talked a lot about my past projects, the Yelp app itself, and the company culture. We discussed some tradeoffs in technologies, and of course, I did whiteboard coding (the recruiter will tell you if it's required, so prepare for that).

In three working days after the interview, the recruiter contacted me to make an offer, which I gladly accepted.

I can't tell you the questions because of the NDA.

If you're comfortable with algorithms (sorting, iterations, find), arrays, trees, linked lists, and all that stuff, you should perform well.

One thing I should mention: practice whiteboard coding before the interview to feel comfortable with it. After about 5 to 10 problems, you'll become okay with the idea of writing code on a whiteboard (if you don't do that in your everyday work, of course), and this should help.