Life cycles,number of eggs per female,minimal adult female length and reproductive costs are presented for 18 species of Amphipoda from the West Spitsbergen area, 77 79 °N. Fifteen species incubated eggs during the polar night and released their offspring in early April. Three species incubated eggs from late spring till late summer. The appearance of the youngest juveniles, indicating the hatching period, is presented for 63 species. Most of the species studied were K strategists, with large eggs of over 1 mm diameter; only one species (Hyperoche medusarum ) was r strategist.