Abstract: The trophic ecology of the large macropods (kangaroos and euros) is summarized. Introduction of livestock has generally favoured the build up of numbers of kangaroos in the arid zone. The reasons are discussed. This paper also reviews work in the arid and semi-arid regions of Australia on diet selectivity of sheep, cattle and goats. Comparisons between the diets selected by domestic livestock and the large marsupials (red kangaroo, Megaleia rufa and euro Macropus robustus) are considered in detail. The degree of competitive interaction and the implications are discussed. Considerable overlap occurs in the diet of goats and cattle, and between sheep and cattle. Sheep, cattle and kangaroos eat similar foods, where there is a wide choice, but the degree of competition tends to be minimized by spatial and temporal separation. Under conditions of severe feed shortage kangaroos and livestock both concentrate on areas supporting the most nutritious forage and competition is intensified.