Metabolic pathways leading to benzylisoquinoline and monoterpene indole alkaloids in plants are revealing remarkable new reactions with potential applications in biocatalysis and bioengineering. Understanding of the enzymatic reactions involved in alkaloid biosynthesis provides access to a variety of applications. In chemo-enzymatic settings, plant biocatalysts can transform medically important scaffolds. Additionally, synthetic biologists are taking alkaloid pathways as templates to assemble pathways in microorganisms that are tailored to the needs of medicinal chemistry. In light of many recent discoveries, it is expected that plants will continue to be a source of novel biocatalysts for the foreseeable future.