This monograph is focused on post-investment issues, particularly on intercultural synergy, and M&A performance. The M&A reasons are the result of globalization, of the need of growth and of achieving synergies. Most of the professionals consider that M&A is one of the most significant business phenomena in the past decades, but warn about the dangers of M&A. The most challenging part of the M&A process is the integration of two entities that present different organisational and national cultures. This monograph emphasises the relationship between culture, post-merger integration processes, and M&A performance. This monograph exerts to find an explanation for M&A performance in terms of the impact that cultural differences have on the post-merger integration process. It emphasises the role of post-investment monitoring and intercultural synergies achievement. This monograph offers an extensive insight of the M&A process inasmuch as M&As are a complex domain demanding an interdisciplinary approach. This book is seeking to deepen the apprehension of the impact of cultural differences on M&A performance. M&A performance can be characterised by ambiguity of the concept and a lack of concurrence on measurement procedures. This monograph reveals that cultural synergy can be produced by similarities in organizations but at once by differences. The empirical results deliver contradictory outcomes. Intercultural synergy might be highly significant after the merger or on the contrary have an insignificant effect on firms' performance or even a negative impact. The findings regarding the cross-cultural integration aspects are contradictory and the relation between M&A performance and intercultural synergy is still to be refined. The findings of this book suggest that intercultural synergy is a significant and controversial issue of cross border M&As. Some inconsistent results suggest the need for further research on post-merger integration. The main goal of this book is to uncover intercultural issues that managers encountered during the post-investment phase and they should have discovered during the pre-investment phase. Intercultural synergy has a strong impact on M&A. Both national and organisational cultures are determinants for maximising the intercultural synergy. This monograph integrates the research on national, organisational and professional culture, into a theory of M&A performance and outcome. It investigates not only the outcomes and intercultural synergy but also the perception on these issues. In the area of intercultural management, this book reveals that the culture clusters make for a very helpful and strong tool. It appears that national culture might influence perceptions on M&A in some culture clusters much more than in others. M&A professionals may benefit from a deeper understanding of cultural values that shape the post-merger integration process and implicitly the M&A performance. The companies that minimise the importance of post-investment monitoring expose themselves to a higher risk of failure. The expectation of the author of this monograph is that the conclusions would help forewarn M&A scholars and practitioners of the need to thoroughly understand the cultural issues influencing the post-M&A processes. This monograph will be useful for academic researchers, postgraduate students, for MBA/Executive Education and for practitioners.