It is argued that HR knowledge is not static but changes according to what is strategically important to organizations. As an outcome of the way managers interpret societal and organizational pressures, and the perception of employees, there are variations in what is valued over time, and in different organizational contexts. The knowledge creation process is influenced by management ideologies and power relationships, and is taken to come from learning by the experience of applying theories and ideas to organizational requirements, often as an attempt to fit HR strategy with business strategy. Four case studies illustrate how HRM attempts to contribute to organizational performance. These suggest that a greater weighting is given to process and diagnostic skills rather than to detailed technical knowledge of HRM. Some of the questions for future research into HR knowledge are discussed, as a consequence of this view of HR knowledge, as dynamic and organizationally specific.