The environment affects the behaviour, physiology, health and performance of domestic animals. The most accessible parameters for study and manipulation are light and temperature. This issue of World Animal Review begins by summarizing the known effects of light and temperature on reproduction in domestic animals. Ewes and goats are stimulated by a reduced length of day, for example, while mares respond to longer days. Genetic improvement particularly through crossbreeding, must be compatible with local conditions (including feed resources), otherwise performance will never match potential. Finally, the unique skin composition of buffaloes makes them much more resistant to high temperatures and allows them to withstand prolonged immersion in water without any harmful effects.