Livestock are key to food security. Meat, milk and eggs provide 34% of the protein consumed globally as well as essential micronutrients such as vitamin B12, A, iron, zinc, calcium and riboflavin. But their contribution to food security and nutrition goes well beyond that, and includes a range of other goods and services, such as animal manure and traction. Hundreds of millions of vulnerable people rely on livestock in a changing climate, because of animals’ ability to adapt to marginal conditions and withstand climate shocks. Livestock products are responsible for more greenhouse gases emissions than most other food sources. Emissions are caused by feed production, enteric fermentation, animal waste and landuse change. Livestock supply chains account for 7.1 GT CO2, equivalent to 14.5% of global anthropogenic greenhouse gas emissions. Cattle (beef, milk) are responsible for about two-thirds of that total, largely due to methane emissions resulting from rumen fermentation. Enteric methane emissions represent 30% of global methane emissions. Because methane is a short-lived climate pollutant, reducing emissions of enteric methane can help mitigate climate change, within our life times.