Anguillid eels have fascinated humans for centuries, but our knowledge of these mysterious fish is still scant. There are 19 species or subspecies in the genus Anguilla, which are found globally, except in the eastern Pacific and southern Atlantic. Their common label ‘freshwater eels’ is a misnomer — all anguillids are facultatively catadromous, born in marine environments, developing in continental waters, with a proportion never entering freshwater at all. Anguillid eels have several life history traits that have allowed them to exploit a broad range of habitats. As such, anguillid eels play an important ecological role in both marine and freshwater environments as well as being commercially valuable. Because of this, anguillid eels are under threat from multiple stressors, such as barriers to migration, pollution, parasites, disease, climate change and unsustainable exploitation. Six species are listed as Threatened in the Red List of Threatened Species, and four are listed as Data Deficient. Strengthening conservation and management of these species is essential, and further research provides an exciting opportunity to develop a greater understanding of this mysterious clade of fish.