Neither freshwater nor marine turtles mate for life. A female turtle often mates with several males before nesting season and then stores the sperm. Because her eggs are fertilized by a variety of males, genetic diversity is high.

Male turtles are aggressive in competing for females. Scratched and bleeding shells are a common sight on females during the mating period. After mating, females come ashore to nest and the males rarely return to land. After a female lays her eggs and has covered them sufficiently to keep predators away, she leaves and never returns to tend to her young. Unlike most birds and mammals, turtles do not form bonds in mates or with offspring.