The focus of this doctoral research is on advancing knowledge of what managers can do to address the issues of corporate cultural differences in mergers and acquisitions (M and A). Despite decades of experience, the rate of MandA failure remains high globally. The root causes of these failures have pointed to inadequate strategic deal theses, excessive purchase prices paid, and poor pre- and post-integration management. Human and cultural factors have also been blamed for these failures. Significant research effort has been expended in raising the importance of human factors and the issue of culture fit in M and A. However, research results have remained ambiguous. Extant organisational M and A culture research has largely focused on examining the role of culture in M and A and its impact on M and A performance. How to address organisational culture differences in M and A is much less studied. Only a small handful of scholars, consultants and practitioners have attempted to prescribe corporate culture alignment guidelines that are either too generic or prescriptive. Managers remain unclear as to how to manage cultural differences in M and A.The research sets out to address how managers can effectively moderate the effects of corporate cultural differences on M and A performance in domestic M and A. It aims to develop a practical M and A corporate culture alignment model for managers tasked with addressing the effects of corporate cultural differences in M and A. It also focuses on addressing the issues of single-layered acculturation of corporate cultures in isolation from the perplexing issues of double-layered acculturation between national and corporate cultures in cross-border transactions. The researcher adopted a qualitative case study research method to deliver on the research objectives within the doctoral research timeframe. He selected a sample of four domestic M and A case studies in Thailand where he is located. Each case study was free of issues related to national cultural differences. The researcher was able to draw rich information and insights from interviewing a total of 50 senior executives, middle managers and staff across case studies. The main research findings provide managers with an improved understanding of the roles of corporate culture on M and A performance and a practical and repeatable five-phase M and A corporate culture alignment model ('5-D'). The model offers a planned step-by-step change approach, key objectives, and suggested tools and templates that help guide managers to effectively moderate the effects of corporate culture differences in domestic M and A from pre-to post-M and A stages. The model also provides strategic choices and implementation guidelines for managers to consider in addressing the emergent nature of acculturation and change in M and A integration situations. The effectiveness of this exploratory model shall be further tested in future qualitative and quantitative studies. The empirical testing of the research recommendations has already begun with a number of recent M and A projects in Asia outside of this research.