Transaction cost economics (TCE), as developed and operationalized by Oliver Williamson, is one of the most prominent and influential developments in the social sciences. In recent years, on the basis of many empirical studies, it has been claimed that the evidence has corroborated TCE. If so, this would have major implications for the debate between TCE and other approaches to understanding the nature of the firm. In this paper we submit the most prominent TCE empirical work to critical scrutiny, on the basis of the standards and predictions in Williamson 's own writings. We find a much more mixed picture, with few studies giving unambiguous support to Williamson's TCE. Furthermore, a significant number of the studies can be reinterpreted in terms of a competence or capabilities approach. We conclude that the empirical evidence does not decisively support Williamson's TCE and we stress the importance of an empirical program of joint testing of rival theoretical approaches. Copyright © 2006 John Wiley & Sons, Ltd.