...
Every SDM student (indeed, every student completing an MS degree at MIT) must write a thesis. You will need to come up with a topic and find an advisor who shares your interest in the topic. Some students prefer to find a cool advisor and then get an idea from that advisor instead of coming up with one on their own: this is OK. Yet other students, especially those sponsored by or working with some organization, integrate their work and thesis together into an in-depth project in some area of interest to the organization (even in this case, though, you must still find an MIT advisor interested in the work).
Start thinking about your thesis early. Especially if you are a 13-month student, you have very little time for thesis research and writing. Don't panic, a lot of people get nothing done until the fall. But you can make your life easier if you start early.
The Thesis Seminar is a small but required course during your first Spring semester. In it, SDM program staff will present ideas and methods for approaching the entire thesis process. They will also bring in professors who have ideas for theses and want to serve as advisors. This is a good way to hook up an advisor early.
...