Arid and semi-arid lands are areas where rainfall is too low or too unreliable for cropping or sown pastures. Australian arid and semi-arid lands comprise a single vast area extending to the 250 mm mean annual rainfall isohyet in the south and the 750 mm isohyet in the north. The grazeable areas are used for grazing of sheep or cattle under very extensive management, producing wool and meat for export. The industries have a low production per unit area, but are very efficient in terms of production per unit of labour. Graziers and administrators have had an overoptimistic perception of the land and climate which has led to varying degrees of resource degradation. Applied research into resource inventory, range condition and trend, stock carrying capacities, and droughts is described. The land and climate of arid and semi-arid Australia are comparable with those of other parts of the world, but socio-economic factors are very different.