Feed-efficient ruminant production is a key topic in the further development of ruminant husbandry all over the world. Ruminants contribute substantially to human nutrition by production of milk and meat. They are also extremely useful for mankind by providing other important products and labour, such as skins, clothing, bones, dung, heating material, and working as draft animals, etc. The microorganisms in the rumen of ruminants are able to process lignocellulose from low quality roughage into volatile fatty acids and energy, to transfer non-protein nitrogen, such as urea, into microbial protein, and to synthesize B vitamins. Therefore, ruminants are able to produce food of animal origin without competition for feed with non-ruminants and man. On the other hand, gas methane (CH₄) with a high greenhouse gas potential is an unavoidable by-product of rumen fermentation. Furthermore, growing ruminants are characterized by a low growing potential (daily yield in edible protein < 0.05% of body weight). The objectives of ruminant breeding, nutrition and keeping/management should, therefore, be to maximize/optimize the advantages of ruminants and to minimize their disadvantages. Feed-efficient ruminant production is viewed as a complex system starting with plant and animal breeding. More systemic approaches are considered necessary to understand interactions and to find acceptable solutions for complex relationships in the context of food security, resource efficiency, as well environmental, social and economic aspects.