Mixed crop–livestock systems produce most of the world׳s milk and ruminant meat, and are particularly important for the livelihoods and food security of poor people in developing countries. These systems will bear the brunt of helping to satisfy the burgeoning demand for food from increasing populations, particularly in sub-Saharan Africa and South Asia, where rural poverty and hunger are already concentrated. The potential impacts of changes in climate and climate variability on these mixed systems are not that well understood, particularly as regards how the food security of vulnerable households may be affected. There are many ways in which the mixed systems may be able to adapt to climate change in the future, including via increased efficiencies of production that sometimes provide important mitigation co-benefits as well. But effective adaptation will require an enabling policy, technical, infrastructural and informational environment, and the development challenge is daunting.