Male octopuses are distinguished from females by the presence of a modified third arm, the third right arm in most species. This arm has a groove running along the edge and a leaf-shaped grasping structure at the tip. When octopuses mate, the male moves elongate sperm packages, called spermatophores, along the groove to the arm tip. The male places the copulatory arm into the mantle cavity of the female where the tip of the arm inserts spermatophores into the female's oviducts. In some long-armed rock-pool octopuses, the male remains hidden, snaking a long modified arm across the rock pool to transfer spermatophores to the hidden female.

During courtship males of some species use complex postures and skin patterns to put on spectacular displays of colour and texture. Often these patterns are only displayed on the side facing the female, while the opposite side of the animal remains camouflaged, presumably as a means of not alerting passing males to the presence of a receptive female in the area. In certain octopuses, the male develops a few very large suckers that may be flashed at females during courtship displays to advertise his maturity, or at males in territorial disputes.

Females of some octopuses can store sperm in special glands for periods of up to three months, until the eggs are mature and ready to be fertilised and laid. Females of all octopuses tend their eggs, continually cleaning them and jetting them with clean water. Females remain with the eggs until hatching, and then die soon after.

In the argonauts (paper nautiluses) and the Blanket Octopus, the miniature male's entire copulatory arm with its store of sperm breaks off inside the female's body cavity. Females have been observed with arms from up to six past suitors, each tip still holding packages of live sperm.