The currency of the Russian Federation is officially the rouble, however the locals will often prefer the US dollar for cash transactions, and you can always expect to get a better rate of exchange if you carry dollars above any other currency.
Credit cards are widely accepted throughout the country, although when making payment you should keep an eye on your card, as there are several scams in operation, where cards are cloned and used.
You should be aware that there are restrictions on how much money you can import and export from Russia without specifically declaring it, and currently these are $10,000 on entry, and $3000 on exit.
