This research applies institutional economics theory to management challenges arising in connection with e-business related transformational change. The research was carried out in response to widely recognised problems in managing IT-enabled change in complex organisations. A cyclic approach builds researcher competence in both the chosen theory, New Institutional Economics (NIE), and its application through a series of four contrasting case studies. The case situations, which derive from the researcher’s work as a technology management consultant, are treated as action research experiments which investigate e-business related transformational change in financial services, retail and government settings. A constructivist stance is adopted within the case situations with the researcher acting as a participant observer. Reflective practice is used to improve the experimental method for the case studies through the course of the research, leading to the use of participatory action research (PAR) for the final case.A literature review of NIE shows it to be loosely defined as a theory, so an analytic NIE framework is created to provide a cognitive model. This model is then modified and extended to produce a final theoretical framework. In parallel, a conceptual map of NIE is created from the research as a practical aid to illustrate NIE concepts and linkages. These two models, the theoretical framework and the conceptual map, evolve through the four case situations which were selected from a range of e-business consulting opportunities available to the researcher over the period of the research. The second case study drives the main development of the two models and draws out the necessary and complementary contributions of both transaction cost economics (TCE) and agency theory (AT) as parts of NIE, neither of which is sufficient on its own. The final case study demonstrates application to practice. The overall sequence of case studies shows the researcher’s cognitive growth from being a novice in the theory and its application in the first case through to a level of proficiency in applying NIE to the rigours of e-business practice in the final case. The research makes several contributions to knowledge. It makes a significant methodological contribution by bringing research methods developed for other forms of professional practice to the management discipline. It also makes a significant contribution to theoretical knowledge. It develops two theoretical models of NIE – a conceptual map and a theoretical framework – which present a way of linking NIE concepts in a meaningful way, and a structure by which NIE can be used in the analysis of highly complex organisational situations. These models clarify the complementary roles of TCE and AT, and indicate a reason why so many studies limited to TCE alone have been inconclusive. Applying NIE to the rigours of e-business management produces, in turn, a contribution to IT strategy formulation.The research makes a practical contribution by showing how NIE can be applied to e-business practice, subject to a number of significant caveats. NIE, as a descriptive theory, is shown to provide a powerful conceptual framework when combined with PAR, although both require deep knowledge and skill. In particular, adopting PAR as a case study method depends on an experienced, skilled and committed practitioner for its effective use.Finally, the research finds that NIE’s strengths as a framework for strategic analysis of large scale and complex e-business situations involving transformational change, which make it unduly sophisticated for less challenging situations, mean that NIE is suited to use by highly skilled, specialist consultants rather than by general managers.