Corporate mergers and acquisitions (M&As) are prominent means for corporate strategy. In many M&As information systems (IS), integration is critical for achieving the intended goals. By integrating previous research on M&A and IS integration, we develop a six-dimensional theoretical framework for IS integration in corporate M&As. The framework is used to describe and explain IS integration management in four M&As. Based on the four cases, the theoretical framework and the existing literature, an initial model (Dynamic System of IS Integration in M&A, DySIIM) describing and explaining how IS integration relates to the M&A process is developed. Through the combination of the DySIIM's dimensions, the dynamics of different parts of the M&A process are captured. The model can be used in further research to build cumulative knowledge about how to manage IS integration in M&A. The model can also be used by companies in their M&A since through the combination of dimensions, it shows the IS integration issues, decisions and actions that a company has to address in the process.