Widespread in nature, mutualistic associations –cooperative interactions between unrelated species– are linked to major evolutionary transitions, and are pivotal for ecosystem functioning. The evolution and subsequent stability of mutualisms has long been a riddle: while they are thought to be prone to breakdown, some have persisted for millions of years. In this talk, I will focus on mutualistic dependence – the degree to which a partner is dependent on the interaction for survival or reproduction. Drawing from examples from my research using ant/plant symbioses, I will ask how highly vs. lowly dependent mutualisms maximise returns from their partners and deal with associated trade-offs.