Contemporary career mobility models do not fully explain up-or-out promotional systems in professional service firms (PSFs). We propose a PSF career mobility model, which represents hiring decisions as investments in options on future human capital acquisitions and promotions as exercise of those options. Promotional outcomes depend mainly on the development of employee's human capital and business conditions at the time of partnership consideration. The model explains seemingly paradoxical firm behavior, such as dismissal of nonpromoted but productive employees. Career mobility in organizations continues to receive a good deal of attention in the management literature. For example, promotion interdependence (Barnett & Miner, 1992), managerial career development (Demougin & Siow, 1994), promotion/turnover relationships (Johnston, Griffeth, Burton, & Carson, 1993), promotion equity (Schwarzwald, Koslowsky, & Shalit, 1992), and tournament mobility (Sheridan, Slocum, Buda, & Thompson, 1990) have been the subject of contemporary researchers' investigations. However, most of this work has been conducted with respect to classical business firms, in which ownership, management, and production functions are separate; promotions entail incremental advancement along multistep job ladders; and nonpromoted individuals are typically retained in their current positions (Kilbourne, Miller, & Cardinal, 1993). It remains unclear whether theoretical models developed in this context should apply to professional service firms (PSFs), in which ownership, management, and production functions are concentrated among the same persons; promotions entail few, large steps toward partnership; and nonpromoted individuals historically have left the organization pursuant to an "up-or-out" rule (Nelson, 1988). The up-or-out system perhaps most distinguishes professional service organizations from other types of firms (Maister, 1982). Nevertheless, despite prevalence of this system in organizations ranging from law, The authors wish to acknowledge valuable comments from Jeffrey B.