The EU’s membership status, i.e. how it can and does act in international organisations, varies significantly. There is no single determinant that is able to explain this diversity. Neither the IOs’ membership rules, nor the position of third states vis-à-vis the EU’s status, the EU’s legal competences, or internal preference distribution offer a satisfactory explanation. This chapter analyses the EU’s membership status in eight key IOs in the socio-economic sphere (GATT, WTO, OECD, DAC, G8, G20, ILO and FAO).1 It shows that the EU’s status in IOs is varied, but has remained remarkably constant over time in each IO. To a large extent, the EU’s current status in IOs is determined by the ‘initial decision’ made on the basis of the legal and political, internal and external contexts at the time. Changes to these contexts have not altered the EU’s membership status in the cases of the GATT/WTO, OECD/DAC, G8 and ILO. However, in the cases of the FAO and G20, two critical junctures – short periods of rapid contextual change – have enabled a significant upgrade of the EU’s status.