The depletion or accumulation of metabolites in the tumour microenvironment is one of the hallmarks of cancer, but targeting cancer cell metabolism therapeutically must also take into account the impact on metabolic pathways in immune cells. As we understand more about immunometabolism, opportunities arise for synergies between agents that modulate metabolism and immunotherapy. In this Review, we discuss the pivotal role of metabolic pathways in both cancer and immune cells in shaping the tumour microenvironment. We survey major anabolic and catabolic pathways and discuss how metabolic modulators and dietary nutrients can improve the anticancer immune response and overcome drug resistance mechanisms. Agents in the clinic include inhibitors of the adenosine and tryptophan pathways, and we discuss opportunities and challenges for successful drug development in the context of immune checkpoint blockade and chimeric antigen receptor (CAR)-T cell therapies.