Although the HRD literature is fairly consistent in affirming the recognition that employee learning is critical to organizational performance, there has been little agreement about how best to demonstrate the contribution of employee learning to the organization's bottom line, with approaches varying from industry to industry and from organization to organization. Focusing on the professional services sector, an industry sector that has garnered little attention in terms of HRD measurement research, this paper draws on the analytical techniques from Grounded Theory to explore how 15 professional service firm (PSF) decision‐makers who are responsible for their firm's learning and development strategy measure the business impact of professional employee learning. The outcome of this study is a preliminary theory, grounded in the interview data, that explains what learning opportunities are offered to professional employees and why, how the business impact of professional employee learning is measured, and how PSF decision‐makers use those business outcome measures to make decisions. The unifying theme emerging from the study is Win Rate, a composite of multiple quantitative measures that include direct as well as indirect contributors to the firm's bottom line. Implications of our findings for HRD research and practice are also addressed.