North American reindeer (Rangifer tarandus tarandus) are seasonally polyestrus short-day breeders. Seasonal ovarian activity begins in late August with an estrous cycle length of 24 ± 3.4 days. Estrous synchronization protocols have been published and are similar to protocols in sheep and goats. Artificial insemination has been met with limited success in North American herds. Further studies are needed to establish methods and protocols that provide acceptable conception rates. Pregnancy status can reliably be determined using ultrasonography and serum detection of pregnancy-specific proteins. Gestational lengths vary greatly with reported ranges of 198 to 240 days. During the rut, male reindeer will often cease eating altogether. They exhibit extreme aggression, and even the most docile males cannot be trusted. Rutting behavior includes a grunting behavior accompanied by hunching and urinating on the hind feet. Semen cryopreservation continues to be a challenge in reindeer, with most frozen-thawed samples having very poor motility.