Tropane alkaloids are found in a scattered distribution among the angiosperm families including members within the Solanaceae, Erythroxylaceae, Convolvulaceae, and Brassicaceae. Recent studies regarding the origins of tropane production provide strong evidence for a polyphyletic origin, suggesting that novel enzymes from different gene families have been recruited during the course of flowering plant evolution. Tropane alkaloid biosynthesis is best documented on the molecular genetic and biochemical level from solanaceous species. Regardless of the system chosen, there are currently gaps in the knowledge of enzyme structure-function relationships and how they influence tropane alkaloid biosynthesis. Obtaining insights on structure-function relationships of tropane biosynthetic enzymes is critical to understanding regulation, turnover, and flux of metabolites through the pathway. In this review, we discuss the current state of knowledge regarding structure-function relationships of the known steps involved in tropane biosynthesis.