In this book we address the complex cooperation between physicians and managers in hospitals by studying their deeply embedded professional differences and its influences on hospital performance. We describe the results of our culture gap questionnaire. With the "GAHP-questionnaire" we can quantitatively elaborate on the size and content of differences between physicians and managers. We apply intergroup theory to the hospital context in order to add a perspective into the known complex relationship between physicians and managers in hospitals. The stereotypical gap questionnaire enables quantitative measurement of the strength and size of stereotypical gaps between physicians and managers. Furthermore we analyse the intragroup variability within groups of physicians and managers in order to identify subgroups that can be focused on when setting out to improve cooperation with the other group to implement organisational change. In the last chapter we statistically associate the cooperation to quality performance in order to search for areas of performance that are influenced by their complex cooperation.