There are several varieties of ferrets, based on coloration. Fitch ferrets (the most popular) are buff-colored, with black masks, feet and tails. Albino ferrets are white, with pink eyes. There is also the Siamese ferret. The female ferret is called a "jill", while the male is called a "hob". Babies are "kits".

The gestation period of ferrets is 42-44 days (average, 42 days). The average litter size is 8 (range, 2-17). Kits are born deaf, with their eyes closed. Their eyes open and they begin to hear between 3 and 5 weeks of age. Their deciduous ("temporary") teeth begin to erupt at 2 weeks of age, at which time they begin to eat solid food. Kits generally are weaned onto commercial kitten chow at 4-8 weeks of age. Kits reach their adult weight at 4 months of age. Males are typically twice the size of females, but both sexes undergo periodic weight fluctuations. it is not uncommon for the average ferret to add 30-40% of its body weight in fat deposited beneath the skin in the fall, and lose this fat the following spring. The average life span of ferrets is 9-10 years.