Barley is a highly significant feed grain, especially in colder regions where other feed grain crops such as wheat, sorghum and corn cannot easily grow. It is used to feed ruminant and non-ruminant species. Despite 80% of the worlds barley being used as feed, most of the emphasis on breeding and selection has been focussed on supplying the malting and brewing industries. This chapter discusses the concept of “feed barley, along what is expected from barley to be used as feed for a range of livestock. The chapter then reviews ways of optimising the use of barley for animal feed, from production and breeding through to the application of new technologies such as near infrared spectroscopy and molecular markers. The chapter then examines the specific grain quality and nutritional requirements of the major animal species routinely fed barley-based diets. The chapter concludes by assessing future research trends in optimising the use of feed barley.