Soya bean and canola meal are the conventional ingredients used to provide protein in poultry feed. However, they are relatively expensive and must be imported to many poultry-producing areas. Developing alternative protein sources for poultry nutrition will reduce the pressure on these key protein sources, as well as promote the development and sustainability of the poultry industry. In this chapter, we first review the supply of conventional protein sources for poultry, and then consider the range of alternative protein sources that might be developed, including grain by-products, oil seed and fruit by-products, pulses, algae, duckweed and certain animal protein sources. We consider how birds respond to diets containing alternative protein sources, and provide recommendations for improving the nutritive value of these alternative sources.