The grain-based ethanol production has been increasing as the demand for biofuel additives increases. This has generated co-products which provide a potential alternative livestock feed source, notable wet distillers grains with solubles (WDGS) and dried distillers grains with solubles (DDGS). After introducing production methods for distillers grains, the chapter assesses the nutritional properties of distiller grain products as well as methods for assessing product nutritional quality. It then reviews issues relating to feeding distiller grain products to ruminants (beef and dairy cattle) as well as monogastric species such as swine and aquaculture species.