Polychaetes of the family Syllidae exhibit a remarkable diversity of reproductive phenomena. The primitive mode of sexual reproduction is characterized by epitoky (as epigamy and stolonization, respectively), swarming and external fertilization. Deviations from the primitive type, particularly evident in meiofaunal species, include external brooding, direct sperm transfer, internal fertilization, viviparity, parthenogenesis, and simultaneous as well as successive hermaphroditism. True asexual reproduction is rare. The first part of the paper gives a survey of the various reproductive modes in syllids, with special reference to recent results. The second part focuses on the mechanisms of environmental and physiological control of sexual reproduction.