Gametes, also known as sex cells or germ cells, are the cells that come together during fertilization or conception in organisms that reproduce sexually. The gametes of females are called eggs, the gametes of males are called sperm. In diploid species, each contains only one set of chromosomes, meaning that they are haploid. When a sperm and an egg fuse, they form a zygote, a diploid cell, which through multiple divisions and differentiation develops first into an embryo and ultimately into a mature individual.

The somatic cells of the offspring will carry one copy of the chromosomes from the father's sperm and one copy of those from the mother's egg. A gamete's chromosomes are not duplicates of either of the sets of chromosomes that are carried in the somatic cells of the individual that produced the gametes. Rather they are hybrids, which are produced through the recombination or crossing over of chromosomes that takes place in the making of gametes ("meiosis"). This hybridization has a random element, such that in every gamete an individual produces the chromosomes tend to be unique. This accounts for the genetic dissimilarity of siblings.

Organs that produce gametes are called gonads in animals, or archegonia and antheridia in plants.