 Numerous studies have shown that many surgical site infections SSI are preventable with appropriately timed antimicrobial prophylaxis. Patients receiving prophylaxis either well-before or well after surgery are up to 5 times more likely to develop an SSI than those receiving appropriate therapy Classen et al, 1992. Unfortunately, errors in antimicrobial prophylaxis timing are extremely common with error rates typically reported to be between 35 and 40. Given that errors in antimicrobial prophylaxis are common and the consequences of error so grave, identifying methods to assist hospitals in improving prophylaxis must be a high priority. TRAPE will evaluate a multifaceted, theory-based intervention to assist hospitals in progressing through stages of organizational change to improve the prophylaxis process. We will test the impact of the intervention using a rigorous group-randomized, nested, pretest-posttest design Murray, 1998. 