The tropane alkaloids are an important class of natural products distributed in different plant families that are found throughout the world and have a wide application as various remedies. In this chapter, the tropane alkaloids are classified according to their subsequent biosynthetic pathway of formation, following the same general lines as before. From this point of view, the alkaloids are described as derivatives of four main intermediates—tropinone,  methylecgonone, 4-benzyltropanone and pyronotropane. Our focus is on the biosynthetic pathways of tropinone and  methylecgonone derivatives, the largest group of tropane alkaloids, typical for family Solanaceae, Convolvulaceae and Erythroxylaceae, as progress has been made in this field after more than a century of research. The biosynthetic pathways leading to the five tropinone subgroups, the mono-, di- and tri-substituted tropanes, the epoxytropanes and the calystegines, are described in detail. Within each subgroup, the most important representatives of pharmacological importance are reviewed. Dimeric and trimeric tropane alkaloids are classified as C-C′, N-N′ or C-N′ according to the relationship between the individual monomeric units. The newly found tropane alkaloids with dimeric and trimeric structures are also discussed.