Lions are unique among cats in that they live in a group, or pride. A pride consists of several generations of lionesses, all of whom are related, their cubs, and one or two adult male lions who defend the pride's territory and mate with the females. The adult males are outsiders who may hold the pride for a few months to several years, depending on their ability to defend it against other outsider males. A pride may have as few as 4 or as many as 37 members, but about 15 is the average size.

Each pride has a well-defined territory; where prey is abundant, its area may be as small as 20 square km (8 square miles), but if game is sparse, the territory may be up to 400 square km (150 square miles) in area. Male cubs are expelled from the pride at about 3 years of age and become nomads until they are old enough (at age 5) to try and take over another pride. Many adult males remain nomads for life, however. Some female cubs remain within the pride when they attain sexual maturity, but others are forced out and join other prides. The members of a pride typically spend the day in several scattered groups, though these may unite to hunt or to share in a kill.