Abstract
The Trichoptera World Checklist (TWC) is a project of the successive International Symposia on Trichoptera, with the responsibility for its policy and maintenance assigned to the international Trichoptera Checklist Coordinating Committee. The TWC originated 20 years ago and has been available on the worldwide web for over 11 years, providing ready access to data regarding caddisfly taxa. Security is assured by daily backup of the database. Trichoptera scientists everywhere are urged to continue sending their published research to the Editor. As of June 2009, the TWC included records for 13,574 valid, extant species and 308 valid, extant subspecies in 609 genera of 47 families. It also included 650 valid, extinct (fossil) species, 113 extinct genera, and 8 extinct families. The density of species among biogeographic regions is variable, with known species density in the Oriental Region about 7.5 times that in the Afrotropical Region.