A documented checklist of the Crustacea (Stomatopoda, Decapoda) is provided for the southern Guianas region (sGuianas), a homogeneous ecoregion including Guyana, Suriname, French Guiana and the Brazilian State of Amapá. The history of crustacean collections undertaken there between 1759 and 2022 is summarized. In total, 529 species are listed. Biodiversity varies between countries: 165 species in Guyana; 317 in Suriname, 343 in French Guiana, and 315 in Brazil Amapá, as a direct result of different sampling efforts. There are 22 Stomatopoda and 507 Decapoda, ranked by numerical diversity as Brachyura (206), Caridea (113), Anomura (85), Dendrobranchiata (67) and others (36). The list is analyzed with the species classified by major biotopes, distinguishing those from freshwater, mangroves and estuaries, and frankly marine environments. Regional comparisons are made in the Western Atlantic showing that the sGuianas marine fauna is depauperate compared to that of other regions. This is explained by the influence of the Amazon River plume, carrying desalinated water and fine sediments, which leads to the reduction of coral reef formations in sGuianas. Only a few species of freshwater crabs (genera Kunziana and Microthelphusa) are endemic to the region. The pace of species discovery over the years indicates that the sGuianas fauna remains still imperfectly known and that probably more than 600 species are present in the region.