Registration. At present, you must still register your passport with the OVIR which means the Department of Visas and Registration, (Otdel Viz i Registratsiy) within three workings days of your arrival. If you are staying at a hotel, they will do this for you. If you are living with a friend or in a rented apartment, you too should register with the OVIR in the district where the apartment is located(listed below), especially if you need to extend your visa.

Visa extensions. To extend your visa, you must comply with certain regulations from the very beginning of your stay including registration of your passport and visa. For any extension, you usually need to have an official statement requesting an extension, and if you are staying in a rented apartment or private home, permission to stay a longer time from your host. You then take these papers along with your visa and passport to the OVIR in your district and apply for an extension. It is usually best to have a Russian colleague or friend do this for you.