We open the black box of the M&A decision process by examining whether specialized M&A staff, who perform a wide range of acquisition-related functions, improve acquisition performance. We find that the presence and the quality of specialized M&A staff is one of the most economically important determinants of acquisition performance. We explore mechanisms through which specialized M&A staff improve acquisition performance and investigate why only less than half of US firms employ such staff. Agency costs are a first-order determinant for specialized M&A staff's value-creation role. Such staff do not improve acquisition performance in firms with heightened agency conflicts.