Social welfare and healthcare professionals consider their services fragmented, which also impacts information technology (IT) deployment. They also face the question of whether to cooperate with other organisations in IT. The need to cooperate and to organise cooperation has increased with ever-wider IT deployment. Governance of IT helps in this by defining the responsibilities of cooperating organisations. Improved data sharing and the pooling of developments and purchases are among the envisioned benefits. This article depicts the theoretical basis of inter-organisational IT governance arrangements against the background of a case engaging over 100 organisations. The lessons of the case, including a survey involving 68 experts, suggest that a perceived need to cooperate to achieve concrete benefits and governance principles are necessary to establish inter-organisational IT governance. The findings of this research augment the knowledge base of IT governance with constructs taken from the resource-based view (RBV), transaction cost economics (TCE), and social network theories.