Cities are formalising collaborations across borders at an unprecedented rate: ‘city networks’ now form a wide ecosystem of global partnerships between local authorities that is often underestimated. It might be time to think of city networks more explicitly as institutionalised and presenting a challenging form of more-than-local urban governance. To do so, our essay mixes a review of the overall global landscape (beyond the environmental sector where most of the literature is to be found), with both a network analysis of how these institutions work as a web of connections, as well as an ‘inside out’ view of how they are managed and what the challenges of that are. We do this by analysing a database of 202 of these networks, both statistically as well as via social network analysis. We find that: international initiatives are on the rise, but this context of partnerships has a well-established history, producing a wealth of information and outputs and offering a complex organisational landscape for cities to reach out beyond their local confines. We measure the relationship this has to the integration of cities into the global economy, the pathways it opens for further internationalisation of city leadership and the patterns of partnership with business and international organisations that it implies.