Bees belonging to the genus Trachusa are relatively large, robust species. Females are important pollinators which have a specialised pollen-carrying structure on the underside of the abdomen. Trachusa bees are solitary although usually construct their nests in aggregations. For those species whose breeding biology is known, nest cells are made from resin and pieces of green leaves. Trachusa has a world-wide distribution. This publication is the first comprehensive overview and guide to the 25 Trachusa species found in Europe, Africa and Asia. It provides descriptions of all species and gives separate identification keys to females and males. All species are illustrated, with altogether 205 colour micro photographs and over 50 line drawings showing morphological details. The species accounts are further supported by distribution maps and graphs depicting seasonal occurrences. This publication hereby summarises our knowledge and attempts to stimulate further research in the taxonomy, biology and ecology of this still little-known group of insects.