This document summarizes a presentation on breeding systems for sheep and goats. It discusses purebreeding, inbreeding/linebreeding, outcrossing, crossbreeding, and heterosis. Specific breeding systems covered include two-breed crosses, rotational crosses, and terminal crosses. Advantages of crossbreeding include hybrid vigor, utilizing complementarity between breeds, and producing a uniform product. The document provides examples of historic sheep and goat breeds and influential breeders like Robert Bakewell.