organizational performance with the aim of creating a general framework as a management tool; however, little has been done to show how HR professionals add value to the overall performance of their firms in different contexts. Ulrich, Brockbank, Yeung and Lake (1995), this dissertation extends empirical research on the impact of HR dimension on Business Unit Performance in different change contexts. The methodology applied consists on three basic steps. First, analysis of a unique sample of business units from the third edition of “Human Resource Competencies Study” (HRCS) – conducted by the University of Michigan Business School. Second, statistical testing to find significantly different HR dimensions between the four above-mentioned groups. Third, statistical confirmations of these differences by comparing each pair of groups. The main finding is that in high performing business units immersed in high change contexts, HR stands our in the delivery of certain HR dimensions. In such firms, the HR function is much focused on strategic issues and it plays an important role as Strategic Partner and Change Agent. Furthermore, HR professionals in these firms are seen as specialists in delivering staffing, organization design, setting the direction of change, managing organizational culture and understanding external issues. Therefore, in high performing firms in high change contexts, HR professionals keep track of market information while aligning the human organization to meet external requirements and improve business performance. What makes this finding more interesting is that these HR dimensions show no significant differences between HR departments and HR professionals of the other three groups-high performers in low change, low performers in high change and low performers in low change-.