Got an email from a recruiter because I submitted my resume to a resume pool during a hackathon. Email inquired if I was interested in applying, then set up a phone screen for a few days later. Phone screen was super simple: asked questions about my resume, side projects, hobbies, etc. Was notified at the end of the call that I had progressed to the next step.
The next step was a 1-on-1 technical interview with a developer that worked at MongoDB. We used an online code-collaboration website, and google hangouts. He asked me questions about the classes I was currently taking, as well as general data structures questions. Then I had one coding question. I was notified a few hours later that I had passed this step as well, and scheduled the final interview.
The final interview consisted of 3 back-to-back, 45-minute interviews with different developers, each from a different team at MongoDB. The interviewers were super awesome and informal; we just talked about different Computer Science related things, before they asked me to answer some coding questions.
A few days later I got a call from my recruiter with a verbal offer, and the official offer was emailed to me the day afterwards.
Tip: From talking to several friends who also interviewed, they seem to base questions pretty heavily off what classes you're currently in; I.E. my friends who are in an OS class get OS related questions, those in Algorithms get algorithms-based questions, et.c.