Cross-border mergers and acquisitions (M&A) have become a prominent internationalization and growth strategy of today’s global business landscape. However, the practice faces significant failure in terms of value creation. To this end, the post-merger integration of information systems (IS) is critical for the failure rate of M&As due to the complexity and ambiguity of how and what systems should be consolidated. Research has been carried out to provide frameworks illustrating IS integration methods and the relationship between business strategies and IS integration strategies but omits potential factors that influence the level of IS integration. Hence, the aim of this study is to examine what factors influence how information systems are integrated in cross-border M&As. This was carried out through a qualitative multiple-case study of 9 Swedish multinational corporations with recent M&A activity. The study finds that there are five IS integration methods, one of which was added by this study in order to cover all levels of how IS are integrated. Additionally, a mixture of factors was found to influence specific IS integration methods where the M&A context, design of the IS integration, and organizational characteristics were on a general level found to be most influential. This suggests previous findings focused on alignment of business strategies and IS integration strategies need a nuanced view to further explain the failure rates of M&As.