All foreign guests require a visa to visit Russian Federation. A visa is a document granting permission for entry into the Russian Federation as well as a transit passage through its territory, issued by a consular office in the country of a foreign citizen's residence. This is obtainable from the Consular Section of the Embassy of the Russian Federation, or the Russian Consulate General by submitting.
Please be in mind that the letter of invitation (visa support/visa voucher) and the visa are two different documents. You have to apply first for a visa support and than for a visa. Tourist invitation consists of official confirmation, and a voucher for accommodation bearing the reference number for the Ministry of Foreign Affairs. This may be faxed from a registered organization in Russia.
Visa support costs additionally 700 RUR* per person and requires guaranteed booking in hotel. *For some countries visa voucher can costs more.