For the past twenty five years, economists have been building theories of the optimal management of firms. For example, economic models suggest that under some conditions, piece rate pay raises performance, and under other conditions, promotions tournaments raise performance. Some of these theories have been tested, others have not. Economists are now using new empirical research tools, that we label "insider econometrics," to test the impact of management practices on productivity: to model how much productivity changes; to model why management practices raise productivity; and to examine which firms benefit and why from alternative management practices. The methodology we describe is "insider" because it uses inside knowledge and data from within firms. It is "econometrics" because the methodology is often the application of treatment effects methods to modeling changing management practices within firms. However, the methods and challenges of insider econometrics are unique, and we identify several key features that are important in undertaking empirical studies of workers' productivity. Now that more firms are keeping data on employees, it is time to improve our analysis of the empirical study of the productivity of workers within firms.