In their own words:
Kiva lets you connect with and loan money to unique small businesses in the developing world. By choosing a business on Kiva.org, you can “sponsor a business” and help the world’s working poor make great strides towards economic independence. Throughout the course of the loan (usually 6-12 months), you can receive email journal updates from the business you’ve sponsored. As loans are repaid, you get your loan money back.