The Bureau of Indian Affairs lists 564 recognized Indian tribes as of 2009. Their numbers have increased over the years as they meet the criteria necessary to achieve recognition and reestablish official relations with the federal government. Fifty tribal organizations have been recognized since 1991 alone. Under requirements established by the Federal Acknowledgement Program in 1978, tribes are required to have some sort of officially constituted government as well as a current roll of members determined by some set criteria. If they are recognized, they are eligible for a number of federal housing and health services, among other benefits. Tribes are not required to have a large population, and many of the tribes recognized by the government consist of single villages with just a few inhabitants.