Development economics nowadays is mainstream economics applied to poor countries. An examination of the core principles of mainstream economics reveals tremendous strengths, but also tremendous weaknesses. Other disciplines, such as sociology, anthropology and political science, have complementary strengths that suggest a role for them as equal partners in development studies and policy. The argument for a partnership of disciplines is logical and strong. But cross-disciplinarity is not easy in practice. It is best achieved through concrete exercises which demonstrate exactly how “two disciplines are better than one” when analyzing specific policy issues in development.