It’s quite difficult to find a place to stay in Heidelberg because many students are looking for a flat at the same time. But if you start your search as early as possible there is no need to worry. These websites should be helpful:

• Check out WG-gesucht, Studenten-WG, Kalaydo or ImmobilienScout24 to look for flat shares (“WG”) or small apartments for just one person. You might have to ask someone to translate.
• During the semester holidays (February, March, July, August) many students post their old flats or rooms on Facebook.
• Apply at the international office if you want to stay in a dorm of the Studierendenwerk (small, but cheap).