Chapter 2 is devoted to the relationships between reproduction and life cycle. We start by illustrating the classical division of life cycles on the basis of the alternation of nuclear phases (haplontic, diplontic, haplodiplontic). Then we move on to the alternation between sexual and asexual generations (metagenetic cycles), amphigony and parthenogenesis (heterogonic cycles), gonochoric and hermaphroditic (heterogenic cycles), solitary and colonial, unicellular and multicellular, to conclude with short sections on the alternation of generations dependent on seasonal polyphenism and the different ways in which different reproductive phases can be distributed within one generation.