First a brief phone call with HR to get info about the company, career options and gauge your interest. Second is a HackerRank coding test consisting of 2 problems, with 3h to solve them, which means you need to pass most if not all unit tests (which are not published). While most tests are testing correctness, there was at least one that tests performance and fails for a brute-force slow implementation. If the test went well, a technical phone interview follows. Mine consisted again of a brief intro to Two Sigma, followed by series of technical questions, followed by an opportunity for me to ask questions. Knowing/remembering CS basics is helpful, O(n) stuff, hashing, trees, design patterns, etc. After that you'll be invited for a day of in-person interviews, where the first half of the day consists of mostly technical interviews. I was sitting on a computer with the interviewer fixing a broken implementation and writing unit tests using Eclipse. In another interview, I designed a game on the whiteboard and later implemented it in Eclipse. You'll be taken out to lunch while the team discusses how well you did and whether they'll call you back for afternoon interviews. I was asked back and had 3 further interviews with managers in 3 areas for which I was a potential fit. Questions were a lot higher-level then. A 4th discussion is with HR to go over what comes next. I was called back after a few days by HR with the good news that they hoped to get me on board but wanted further information. I had yet another interview, followed by some preliminary comp discussions followed eventually by the offer package. To prepare for this and many other technical interviews, I found the book Cracking the Coding Interview very helpful, it goes over some basics you might've forgotten in the last n years of work, with good advice on prep, test taking, design, etc. A good understanding of unit tests will be useful, too. I've found the Two Sigma HR people to be helpful and responsive. They are ramping up their employee count like crazy, I'm sure that's contributed to certain inefficiencies others have reported.