IntroductionT his article examines the determinants of the size and role of HR departments within firms, according particular attention to the effects of objective factors, including organizational size, sector, and the national context. At the heart of this study is a desire to understand the relationship between the relative resources and importance assigned to the HR function and its social context. In other words, the study explores the relative size of the HR department and the manner in which strategic HRM policy and practice is constrained or enabled by setting. Are some settings more likely to engender a proactive strategic HR role? And, in others, is the HR role likely to be reactive, predominantly administrative, andWhat determines the resources allocated to an HR department? The antecedents of the size of HR departments within firms and the relationship between HR department size and the role that HR departments perform are issues of theoretical and practical importance. Using large-scale survey data from organizations in Europe and Japan, this article explores the influence of nationality, size, and sector on the comparative ratio of HR specialists in organizations, and on the likely scope and brief of such departments. It also examines the internal organizational characteristics associated with HR department size. In contrast to previous literature on administrative components, we demonstrate that the human resources staff component is affected not only by organizational size but also by sector and national location.