This theoretical study contributes to the debate in the field of strategic HRM on whether HRM systems should differ across employee groups within the firm. It explores differences in the efficacy of two HRM systems—high-involvement HR and internal labor market systems—across top management teams, middle managers, and professional employees. In addition, it examines factors that may prevent the adoption of effective HRM systems for these groups of knowledge workers. A model is proposed depicting how four job-level moderators influence the HRM-performance relationship and how these moderators apply to each of the three employee groups. Short-term performance pressures and favoritism in staffing are proposed as factors that may hinder the adoption of effective HRM systems. Finally, HRM systems for different employee groups are classified based on their gains potential and barriers to implementation, yielding four categories of strategic HRM activity metaphorically labeled low-hanging fruits, high-hanging fruits, peanuts, and barren land. © 2013 Wiley Periodicals, Inc.