Accommodation in Hannover

The International Office published a list with several possibilities to find accommodation, you find it here:

Additionally, here is some advice from students for students!
It can take a while to find a shared flat here in Hannover, so we recommend that you apply for a dormitory room as soon as possible. The dorms which have the most available rooms are not located within the city center. However, the middle of the city and the university is easily accessible through public transportation, which runs the entire night on weekends! The dorms are also wonderful places to meet new people and enjoy time outdoors!
If you prefer to life in a shared flat (or you are too late to apply for the dorms), is the most important website for you. On this website, students and other young people are searching for new flatmates. If you want to apply for a room in one of these shared flats, write a short text about yourself to contact your potential flatmates. If they like what you have to say, they will invite you to a “casting”. Because there are so many nice and friendly applicants for one room, you’ll have a better chance of being chosen if you can make it to the casting in person instead of doing an interview over Skype. After the castings, they’ll choose who they liked best. As stated above, there are a lot of people who are looking for places to live in Hannover, so it could take you a while to find a flat. Just keep trying and don’t give up!
Your chances of finding a room might be better if you apply for a room in a flat that is only available for a certain period of time. This is called a “sub-lease” or in German, “Zwischenmiete”. This happens when a German student, for example, is studying abroad themselves and wishes to rent their room to someone else for a semester or two. Another advantage to these rooms is that they tend to be fully equipped with furniture. People who are renting rooms for indefinite periods of time are typically looking for someone who will stay longer than a year, and you might end up having to buy your own furniture.
You can also publish a request, or “Gesuche”, at wg-gesucht. This will probably not result in offers from the coolest shared flats in town, but you might be contacted, for example, by elderly people looking to rent rooms to students. It’s free of charge, so it’s definitely worth a try!