There has been a dramatic expansion of global livestock production over the past 60 years or so. This increase in production has been driven partly by growth in the human population but also by changing demand associated with growing affluence in some countries, lower relative cost of many livestock products, urbanisation and increasingly global food systems. While this expansion of production has contributed to global food and nutritional security and livelihoods, it has also had significant negative environmental and ecological effects. Biodiversity loss and greenhouse gas emissions are especially important, with global food systems ranking as the first and second most important drivers of these, respectively. This chapter briefly reviews the evidence for the adverse and beneficial effects of livestock production and explores opportunities to improve the sustainability of livestock systems.