Congo uses the Central African franc (CFA), a stable currency also used by five other countries in the region. It's pegged to the euro at an unchanging rate of CFA655.957. For travellers, euros are the best currency to bring, though you can change US dollars and British pounds in Brazzaville and Pointe-Noire. Banks willing to exchange money are rare outside these cities, but businesses owned by Lebanese and West Africans usually change money, though rates will not be competitive. Whichever currency you bring, make sure your foreign bills are in pristine condition.
Crédit du Congo, Ecobank and BGFI Bank all have ATMs in Brazzaville and Pointe-Noire that accept Visa, MasterCard and Plus cards.
While a relatively new concept in Congo, tipping is now expected in fancier places. Around 5-10% is normal in good restaurants. Guides and resort staff will also usually expect something – there's normally a staff tips box in top-end places. As rates are normally negotiated before the journey begins, taxi drivers do not need to be tipped, though some may ask for one.