The development of law and economics is a success story in the expansion of economics into other social sciences since the 1960s. The success has been attributed to the fact that economics offers a powerful set of analytical tools with a forceful theory of human behavior. But if this is the only reason, then the move of economics into other social sciences such as political science and sociology should have been equally successful. This, however, has not been true, and the discrepancy calls for an explanation. The commonalities between economics and law in both subject matter and analytical approach provide a more convincing explanation; some of the difficulties faced by the legal economists can also be explained by an appreciation of the commonalites between economics and law.