Lobsters mate in a shelter during the summer when the female has just moulted and her carapace is still soft. The male turns the female over on her back and transfers his sperm cells into the female using his first pair of swimmerets (gonopods). After the mating is over, the male puts the female back on her legs and protects her for a few days, enough time for her carapace to harden. After mating, the female keeps the male's sperm for several months (up to one year and even more).

For most females, the eggs will be laid the year after mating. The eggs are fertilized outside the female when the eggs are laid. After they’re laid, the eggs remain attached under the tail, on the pleopods, by a kind of sticky substance. The female then keeps her tail folded up under her and carries her eggs for almost a year (between 9 and 12 months). Therefore, females mate approximately once every two years. A female can lay a few thousand eggs when she is young and several tens of thousands of eggs when she is older.

Females can lose up to 50% of their eggs during the incubation period. These losses can be caused by disease, parasites, predation, or by fishermen repeatedly catching, handling, and then releasing egg-bearing females.