We examine how two types of slack resources relevant to knowledge employees—human resource slack and financial slack at the R&D functional level—influence the rent-generating potential of firm-specific knowledge resources. According to the resource- and knowledge-based views of the firm, firm-specific knowledge resources are critical for generating economic rents for a firm. However, without motivated knowledge employees investing in the corresponding specialized human capital in the process of absorbing and deploying firm-specific knowledge resources, the resource potential for rent generation would be greatly discounted. We argue that human resource slack among knowledge employees and financial slack available for R&D activities affect the rent-generating potential of firm-specific knowledge resources by influencing knowledge employees’ incentives to invest in specialized human capital. In particular, while financial slack facilitates rent generation of firm-specific knowledge resources by increasing employee incentives to invest in specialized human capital, human resource slack hinders it by reducing such incentives. Empirical results based on longitudinal R&D employment data, U.S. patent data, and Compustat support these arguments.