Three native crayfish species live in Switzerland: Austropotamobius torrentium, Austropotamobius pallipes, and Astacus astacus. A. torrentium occurs in many brooks in the northeastern part of Switzerland. A. pallipes lives in brooks, canals, and ponds in the western part of Switzerland and in the valleys of the alpine region. Many populations of both species have disappeared. The full extent of this decrease is not documented. A. astacus can be found in many lakes, ponds, rivers and brooks throughout Switzerland. Cultivated ponds have been restocked after population collapses. Four introduced species live in Switzerland. Astacus leptodactylus can be found in many lowland lakes and ponds at present. Orconectes limosus forms strong populations in the western part, that are spreading eastwards along the River Aare and can be found in single populations in several parts of Switzerland. Pacifastacus leniusculus has been found in a few ponds, in Lake Geneva, in two brooks and in the River Aare. Procambarus clarkii lives in four ponds in the northern part of Switzerland. The legislation in Switzerland tries to avoid the appearance of alien species and to protect the native species. Possible ways of introduction and the situation of crayfish species in Switzerland are discussed.