In this dissertation, I study the role of labor supply in macroeconomic fluctations and the movement of employment in response to these fluctuations. The first chapter is a theoretical and empirical study of the role of firm-specific labor supply in amplifying business cycles. The second chapter focuses on measuring the aggregate labor supply elasticity at the extensive margin, using a novel survey approach. Finally, in the third chapter I measure the effects of government policies in the early stages of the COVID-19 pandemic on employment, using decentralized implementation of these policies.In the first chapter, I assess the role of labor market monopsony---finitely-elastic firm-specific labor supply---in the context of a New Keynesian mo...