3D printing affords the laboratory chemist unprecedented freedom to design and fabricate bespoke chemical reactors uniquely designed for specific purposes. This video demonstrates the design process of creating 3D-printed reactionware, and describes how we have used these devices to control not only the chemical environment of a reaction (the incorporation of catalysts and reagents into the structure of the reactor) but also to use the architecture of the chemical reactor itself to influence the trajectory of chemical reactions. The use of this design and fabrication process gives chemists control over their chemistry by manipulating the geometry, topology and composition of their reaction vessel for specific applications.