This chapter discusses three areas of the livestock sector: the importance of the sector, the rich diversity within livestock, and some of the challenges facing the sector. Livestock products are nutritious and culturally important, and meat and animal products contain important proteins, vitamins, minerals and micronutrients that are essential for growth and development. In terms of fats, poultry meat is healthier than red meat. Over-consumption of livestock produce can contribute to obesity. Livestock systems occupy about 305 of the planet’s ice-free terrestrial surface area, have a worth of $1.4 trillion, and employ 1.3 billion people globally. By 2050, the Food and Agriculture Organization predicts that 326 million tons of meat and 585 millions tons of dairy will be required in the developing world. Livestock serve more than just food purposes, serving as religious animals, draft power, providing wool and fabric and other by-products. Livestock can be split into monogastrics and ruminants. Intensive livestock systems have conversion efficiency in that a kilogram of product becomes a kilogram of meat and shows a lower environmental footprint, while extensive systems have high emissions per unit of product, but animal welfare is not necessarily better in either one of these systems. In terms of emissions, livestock are such less efficient than crops, particularly in terms of nitrogen. Ruminants rely on fermentation to produce energy and therefore produce methane, which accounts for approximately 50 percent of all livestock emissions. There needs to be a balance between monogastric industries – with lower levels of emissions, and ruminant systems – which compete less for human edible feed. The final challenge is around matching the system with the environment and the livestock with the environment, an example of which is the Holstein cow.