This article identifies how Belgian civil society organisations (CSOs) legitimise their European networks (ENs). European networks are understood as European umbrella associations gathering together national CSOs and representing them at the EU level. This article unpacks the concept of organisational legitimacy by empirically analysing Belgian CSOs’ discourse about their ENs. EU institutions consider ENs as appropriate organisations to link the European policymaking process to the requests and opinions expressed by national CSOs and their constituents. Existing studies draw negative conclusions about the transmitter role of ENs and highlight the malfunction of the accountability channel and an unfair representative balance among members. This empirical analysis qualifies these two arguments. The results show that Belgian CSOs legitimise their ENs in two ways: the function they hold in Brussels and their efficiency. ENs are thus not legitimised as accurate transmitters between national CSOs and European officials but as efficient champions of general political objectives, to which Belgian CSOs broadly adhere. These results are based on an inductive qualitative analysis of interviews with staff from five Belgian environmental CSOs.