Book excerpt: In the last twenty years there has been an explosion of economic research on labor force dynamics; the movement of individuals between labor force states. This book focuses on the methods by which behavioral theories of labor force dynamics have been empirically implemented. Most attention is paid to the partial equilibrium two-state transitional model of job search behavior. That model is the foundation for much of our thinking about the nature of unemployment at both the individual and aggregate levels. Although the basic formulation has remained the same, approaches to the empirical implementation of such models has changed dramatically.