Three-dimensional printing, also known as additive manufacturing technology (AMT), summarizes material processing techniques, where material is selectively generated according to two-dimensional projections of a three-dimensional (3D) object. These projections are obtained from a digital 3D representation of an object via computer-aided design (CAD). While a range of 3D printing techniques exist for a variety of material classes, inkjet printing and stereolithography summarize all additive manufacturing processes that utilize light to manufacture polymeric materials layer by layer. They both utilize the photopolymerization (photocuring) of liquid photosensitive resins into solid photopolymer networks to spatiotemporally control material deposition but vary with respect to the employed light source and deposition method. This chapter explores the chemistry behind stereolithography, from traditional (meth)acrylic resins to more recent chemistries utilized in the 3D printer. The principles behind different light-based 3D printing technologies is discussed and emerging trends in the field are highlighted. The chapter ends with an overview of analytic techniques for photopolymer network characterization during the polymerization process and of resulting materials post-printing.