Economic development is typically accompanied by a very pronounced migration of labor from rural to urban employment. This migration, in turn, is often associated with large scale urban underemployment. Both factors appear to play a very prominent role in the process of development. We consider a model in which rural-urban migration and urban underemployment are integrated into an otherwise conventional neoclassical growth model. Unemployment arises not from any exogenous rigidities, but from an adverse selection problem in labor markets. We demonstrate that, in the most natural case, rural-urban migration—and its associated underemployment—can be a source of multiple, asymptotically stable steady state equilibria, and hence of development traps. They also easily give rise to an indeterminacy of perfect foresight equilibrium, as well as to the existence of a large set of periodic equilibria displaying undamped oscillation. Many such equilibria display long periods of uninterrupted growth and rural-urban migration, punctuated by brief but severe recessions associated with net migration from urban to rural employment. Such equilibria are argued to be broadly consistent with historical U.S. experience.