From the traditional craft hiring hall to the Web site Monster.com, a multitude of institutions exist to facilitate the matching of workers with firms. The diversity of such Labor Market Intermediaries (LMIs) encompasses criminal records providers, public employment offices, labor unions, temporary help agencies, and centralized medical residency matches. This book analyzes how these third-party actors intercede where workers and firms meet, thereby aiding, impeding, and, in some cases, exploiting the matching process. By building a conceptual foundation for analyzing the roles that these understudied economic actors serve in the labor market, this book develops both a qualitative and quantitative sense of their significance to market operation and worker welfare. Cross-national in scope, this book coalesces research on a set of market institutions that are typically treated as isolated entities, thus setting a research agenda for analyzing the changing shape of employment in an era of rapid globalization and technological change.