Interactions between crops and livestock have been at the core of the evolution of many agricultural systems. In this paper, we identify the development and characteristics of mixed crop-livestock systems, with a focus on grassland-based systems, as these cover large areas in China, and face several challenges. Following the transition from the original hunting and foraging systems to a sedentary lifestyle with integrated crop-livestock production systems some 8000 years ago, a range of different mixed systems have developed, depending on rainfall, solar radiation and temperature, culture and markets. We describe 5 main types of integrated systems: (1) livestock and rangeland, (2) livestock and grain production, (3) livestock and crop – grassland rotations, (4) livestock, crops and forest (silvo-pasture), and (5) livestock, crops and fish ponds. Next, two of these mixed systems are described in greater detail, i.e., the mountain-oasis-desert system and its modifications in arid and semi-arid regions, and the integrated crop-livestock production systems on the Loess Plateau. In general, crop-livestock interactions in integrated systems have significant positive effects on crop production, livestock production, energy use efficiency and economic profitability. We conclude that improved integration of crop-livestock production systems is one of the most important ways for achieving a more sustainable development of animal agriculture in China.