Inland waters are major sources of greenhouse gases (GHGs) to the atmosphere. In this Review, we compile and reconcile current global estimates of CO2, CH4 and N2O emissions from inland waters and place them in the context of the global GHG budget. Estimates indicate total inland water emissions of approximately 8.2 (6.5–10.6; 90% CI) Pg CO2-eq. yr−1 over a 100-year time horizon, despite inland waters only covering less than 3% of the land surface. Mapping of global emission patterns reveals that the largest emitters of GHGs are low-latitude river networks and the numerous small lakes of the Northern Hemisphere. High latitudes, the tropics and very small water bodies have a major role in global fluxes but remain under-represented in observational datasets. Drawing on modelling and budget analyses, we estimate that emissions have increased by approximately 2.8 (2.3–3.5; 90% CI) Pg CO2-eq. yr−1 since the Industrial Revolution, equivalent to an offset of approximately one-third of the land carbon sink. Global inland water GHG emissions are expected to keep increasing throughout the twenty-first century, mainly driven by climate change, but pollution control and careful dam planning could help to limit this increase.