Your Visa to Russia
Every foreign visitor (I. e. somebody who does not hold a Russian passport) needs a visa to enter and exit Russia. Once you have an invitation from an inviting party (your Russian friend, hotel, business partner or a travel company) you need to apply for your visa at a Russian consulate.
There are also restrictions on which embassy you can apply to. Apart from very few exceptions this should be an embassy of your home country or a country of your residency if different. To help you find your local Russian embassy or a consulate Ost-West Kontaktservice has an Embassy Finder page on its website.
Also, document requirements change regularly and it would not hurt to check for any changes in the visa legislation in advance. This is easily done by checking your local Russian embassy's web-page or looking on the websites of tourist companies. Good companies should have regularly updated noticeboards on their websites.
Upon receipt of your invitation you will be required to fill in an application form. Different consulates require various extra documents but generally you need your invitation (in the case of a tourist company inviting you a faxed copy of your invitation is enough), correctly completed visa application form and some photographs of yourself. You will also be expected to pay your visa processing fees. The cost of a visa differs by country and visa type.
