The use of incentives in partnering and alliancing has been seen as an important way of reinforcing collaboration in the short term and helping to build trust between clients and contractors in the long term. Yet only rarely has the impact of incentives on such relationships been discussed, let alone subjected to systematic investigation. This is despite a wealth of theory and research which brings into question the use of incentives and reinforcers as ways of generating motivation and commitment. Drawing upon this theoretical knowledge base and using evidence from a number of case studies of partnerships and alliances, this paper demonstrates how a number of important cognitive and social dimensions affect the use and impact of incentives, sometimes in ways contrary to those intended. The conclusion drawn is that there are important limitations to the use of incentives as means of reinforcing collaboration and developing commitment and trust, and that this raises questions more generally about the assumptions that underlie many of the practical ‘tools and techniques’ commonly associated with partnering and alliancing.