AbstractThe paper presents a survey of Polish malacostracan fauna. In two tables the distribution of freshwater and Baltic species is presented according to the regionalization of the country used in "Catalogus Faunae Poloniae". Figures present some interesting distributions of freshwater malacostracan taxa. Own studies as well as the review of ample literature aimed at the preparation of the successive issues of "Catalogus Faunae Poloniae" allowed to present this survey of 121 malacostracan taxa, viz., Bathynellacea - 1 species, Mysidacea - 9, Amphipoda - 50, Isopoda - 47, Tanaidacea - 1, Cumacea - 1, Euphausiacea - 1, Decapoda - 11. In inland waters 31 species and subspecies do occur (Batynellacea - 1, Mysidacea - 1, Amphipoda - 22, Isopoda - 2, Decapoda - 5). In brackish waters of the Baltic Sea and its lagoons- 54 species (Mysidacea - 8, Amphipoda - 24, Isopoda - 12, Tanaidacea - 1, Cumacea - 1, Euphausiacea - 1, Decapoda - 8). Bi-environmental species are Asellus aquaticus and Eriocheir sinensis. The land malacostracan fauna of Poland includes 4 amphipod and 34 isopod (oniscoid) taxa. The Polish malacostracan fauna is composed mainly of species that have invaded this region of Europe in the postglacial period, but the oldest, preglacial elements are subterranean amphipods (niphargids, Crangonyx) and Bathynella natans, occurring only in southern Poland. The earliest postglacial invaders of the Baltic and/or the northern lakes were glacial relict species like the Mysis relicta group, Pallasiola quadrispinosa, Monoporeia affinis and Saduria entomon. The Southern Baltic malacostracan fauna is dominated by Boreal and Arctic/(Subarctic)-boreal elements but one third of this fauna is Mediterranean-boreal or Lusitanian-boreal in origin. Inland waters were probably settled next by Gammarus lacustris, G. pulex, Synurella ambulans, Asellus aquaticus and Astacus astacus, then by later incomers, like Gammarus balcanicus. Canal constructions in the XVIIIth century helped the immigration of Ponto-Caspian elements: Corophium curvispinum and Echinogammarus ischnus. Intentionally introduced to Polish waters are Astacus leptodactylus, Orconectes limosus and Pacifastacus leniusculus; unintentionally brought along were Eriocheir sinensis and Rhithropanopeus harrisii tridentatus, as well as Talitroides alluaudi and Trichorhina tomentosa to some greenhouses.