While world-wide Mergers and Acquisitions (M&As) activity continues to accelerate, a substantial proportion of deals fails to yield the expected value. The inability to plan and implement post-merger integration of information technology contributes substantially to these failure rates. This paper advances the argument that a company’s pre-existing Enterprise Architecture decisively shapes the capability to implement post-merger IT integration and subsequently realize benefits from M&A. Our multiple-case study investigates three acquisition cases and develops an explanatory theory of how Enterprise Architecture maturity enables the implementation of distinct integration strategies. The results do not only enrich the academic literature on M&A, but also show the strategic value of Enterprise Architecture maturity.