We develop a model to explain why some firms make acquisitions, while other firms with equal performance expectations do not. We argue that the decision to acquire is not strictly a function of expected abnormal returns, but also depends on a firm's unique acquisition threshold. Our model posits that the threshold is determined by governance, managerial competence, synergy with assets in place, and synergy with growth options. Our empirical findings, drawn from a sample of over 27 000 US acquisitions, offer strong support for the model, suggesting that firms with low thresholds may choose to invest despite comparatively low abnormal returns. Copyright © 2007 John Wiley & Sons, Ltd.