The three methods of culturing bovine zygotes; surrogate oviducts, co-culture and defined media are compared and contrasted. Surrogate oviducts provide the best environment and so provide a benchmark to compare in vitro culture systems. At present, co-culture systems provide a convenient method of reliably producing embryos suitable for transfer. This is important for commercial embryo production. The use of defined media is improving and can be as efficacious as co-culture. The advantage of defined culture systems is the ability to find the requirements of an early embryo and to tailor media to meet them. It is suggested that maturation, not zygote culture, may be the constraint in embryonic development.