Plants, which make thousands of complex natural products or specialized metabolites, are outstanding chemists: plants create incredible chemical complexity from simple starting materials. Medicinal plants are known to make molecules that can be used as medicines to cure cancer, pain and other diseases. Here we will highlight how plants make these molecules and how these biosynthetic pathways can be placed into an evolutionary and biological context. We will also discuss methods by which these pathways can be harnessed by metabolic engineering.