Amphipods are unique in the possession of three pairs of pleopods and three pairs of uropods. In a small minority of cases secondary reduction of the abdomen may result in a loss of one or more pairs (e.g. the Caprellidae). No other malacostracan group possesses more than one pair of uropods. The name Amphipoda means ‘different feet’ and refers to the different forms of the pereopods (legs) which contrasts with the related Isopoda meaning ‘same feet’. Amphipods are variously known as, scuds, shrimp or sideswimmers. Those amphipods that have colonised the land are often referred to as landhoppers and beach dwellers are called sandhoppers or beach/sand fleas.

Amphipods range in size from a millimetre in length to the supergiant amphipod Alicella gigantea at 340 mm. Amphipods can be found in all marine habitats (even the deepest ocean trenches e.g. Hirondellea dubia), and have also colonised freshwaters and terrestrial habitats; even ectoparasitic groups are also known among them. There are at least 1870 amphipod species and subspecies recorded from fresh or inland waters accounting for ~ 20 % of the total known amphipod diversity. Amphipods are important herbivores, detritivores, micropredators and scavengers in most environments and they form an important component of marine and freshwater ecosystems.

The World Amphipoda Database arose from a merger in 2010 of the World Amphipoda List compiled over many years by Jim Lowry (Australian Museum), with the European Register of Marine Species (ERMS) amphipod list, compiled by Mark Costello with the help of Denise Bellan-Santini and Jean-Claude Dauvin, and edited up until 2013 with significant additions from the RAMS Amphipoda (Antarctic) list (compiled by Claude De Broyer) and from other regional editors.

The original editors of Amphipoda within WoRMS were Mark Costello, Denise Bellan-Santini, Jean Claude-Dauvin, & Wim Vader, with Claude de Broyer as Editor of the Register of Antarctic Marine Species (RAMS) Amphipoda. The north-Atlantic lists were compiled by Mark Costello with assistance from Louise Collier, from Costello et al. (1989), Brattegard (1997) and Vader et al (1997). The Mediterranean and south Atlantic lists were compiled from Bellan-Santini et al. (1998), Marques and Bellan-Santini (1990, 1991), and Lopes et al. (1993). Additional species were then found in Dauvin (1999), and for Arctic seas, in Palerud and Vader (1991) and Vader (1998). Jim Lowry’s unpublished list was added to WoRMS in 2010 when he became editor of the Amphipoda. To provide sufficient expert knowledge for maintaining the database, we have now (2013) formed an editorial team to whom the queries on particular taxa should be addressed.