In this paper we scanned and summarized the empirical research evidence and found that the effects of pre-licensure interprofessional education on patient/client care are unknown. In contrast, for post-licensure collaboration interventions, there is a growing body of evidence suggesting positive effects on the delivery of care. The coverage of this latter evidence, however, is patchy, being especially weak in primary care. In interprofessional education, where policy level interventions have been value driven for the last half century, we have identified a base of evidence for the effectiveness of certain post-licensure collaboration interventions; this evidence is lacking for pre-licensure interprofessional education. If interventions and policies for both pre-licensure interprofessional education and post-licensure collaboration are implemented without accompanying rigorous evaluation research, we will remain mired in this same uncertainty into the future.