Even though for centuries, international organisations (IOs) have been the preferred vehicle for organising the international community (Magliveras, K. (2020). ‘International organisation’ v. ‘International organisations’: A discourse on synthesis. In L. Boisson de Chazournes et al. (Eds.), Liber Amicorum en l’honneur de la professeure H. Dipla (pp. 513–531). Editions A. Pedone.), the number of regional IOs has constantly been rising, and their significance in transnational dealings has been increasing. But the question of their competition has not been discussed at length. Arguably, this has deprived the epistemic community of regional IOs of significant elements in determining and analysing the behaviour, qualities and characteristics of regional institutions and those participating in them, as well as the dynamics that are created. This essay attempts to lay down the fundamentals for an advanced discussion of competition among regional IOs, accepting that competition simply emerges when several IOs operate in the same domain (Arora-Jonsson et. al., 2020). By examining competition from a legal and not from an international relations perspective (Downie, Review of International Studies 48:364–384, 2022) and by using terms and norms from European Union (EU) competition law (e.g. products/services, geographic market, relevant market, undertakings, customers, demand, supply, market entry/exit, dominant position, monopoly), the essay argues that those IOs operating within a given area/region and exhibiting common features and traits constitute a market, effectively a competitive environment of functionally overlapping institutions (Gehring and Faude, The Review of International Organisations 9:471–498, 2014).