We studied the life history of tardigrades with a particular focus on the maturative patterns of the ovary and testis. Specimens collected in nature belonging to four species of one freshwater and two semiterrestrial genera of eutardigrades were examined. The females of all examined species are always iteroparous; they have several maturative cycles with synchronously developing oocytes. Four maturative stages can be distinguished in each ovarian cycle, which is clearly correlated with moulting. In contrast, gametocyte maturation does not seem to be correlated with moulting in males and varies markedly in the considered genera. The testes of adult specimens ofMacrobiotusalways contain both mature spermatozoa and cells at earlier stages in spermatogenesis (continuous maturation). The testis ofPseudobiotus megalonyx, the only freshwater species examined, shows a gradual increase in spermatozoa that in the end completely fill the gonad (progressive maturation, tied to a semelparous life cycle). The testis in adult males ofAmphibolusis either filled exclusively with spermatozoa or alternatively with immature germinal cells, revealing an iteroparous condition similar to that of the females (cyclical maturation). The different types of gonad maturation in males seem to be correlated with habitat and the capacity to enter cryptobiosis.