The search for low cost, nutritive ingredients for animal feeds has led to consideration of the possible harmful or beneficial effects of secondary plant products. This book presents the papers delivered at a MAFF conference, and contains overviews of secondary plant products in general, and tannins, trypsin inhibitors and lectins in particular. Contributors have been drawn from academia and industry, and include animal nutritionists and plant breeders. In the concluding discussion, an attempt has been made to identify future research needs. What emerges is the need to be precise about the identity of the secondary plant product present, its effects, better and relevant analyses, and to be mindful of the different needs of pigs and poultry, compared with ruminants.