The local unit of currency is the Kenya Shilling which these days is freely convertible within Kenya for the U.S.$ and other currencies. There are numerous banks and bureaux de change in towns, and most lodges and hotels will exchange currency or travellers cheques at reasonable rates.
It is not possible to obtain Kenya Shillings outside the country, and it is illegal to export more than a small amount. Many items or services are priced and paid for in US dollars so do not convert more funds into the local currency than you need for incidental expenses.
Credit cards are accepted at an increasing number of establishments in Kenya but not everywhere. It is not generally possible to obtain cash on a credit card in Kenya, so it is recommended that visitors carry sufficient funds in the form of travellers cheques.
You should take most of your money in travellers cheques from a well known company such as American Express or Thomas Cook. US Dollars or Pounds Sterling are recommended. It is advisable to carry some US dollars cash in small denominations. Well known credit cards such as Visa, Mastercard and American Express are accepted at many hotels and tourist shops.