Despite the proliferation of HRM research, only a small fraction explores the context of small and medium-sized enterprises (SMEs). Where HRM in SMEs has received attention the literature base remains fragmented and variable, comprising a plurality of definitions, explanations and methods. To advance understanding, this paper uses a quarter-century systematic review drawing on an evidence base of 137 peer-reviewed articles. A cumulative framework is presented capturing key developments and synthesizing existing areas of research focus. Analysis of limitations and knowledge-gaps finds a failure to differentiate across various types of SMEs, limited appreciation of SME characteristics and contextual conditions, and a dominance of managerial perspectives. An agenda for future research on HRM in SMEs is outlined with respect to definitional parameters, HR practices, HRM-Performance, key determinants and presenting issues. The paper concludes that SMEs offer a unique, fruitful and timely context for investigations of HRM.