Although managers cite human resources as a firm's most important asset, many organizational decisions do not reflect this belief. This paper uses the VRIO (value, rareness, imitability, and organization) framework to examine the role that the Human Resource (HR) function plays in developing a sustainable competitive advantage. We discuss why some popularly cited sources of sustainable competitive advantage are not, and what aspects of a firm's human resources can provide a source of sustainable competitive advantage. We also examine the role of the HR executive as a strategic partner in developing and maintaining competitive advantage within the firm.