Three-dimensional (3D) printing is a process of fabricating 3D objects by adding successive layers of materials (e.g. polymers) on top of each other. Among various 3D printing approaches, the photochemical approach is extremely attractive as objects can be produced via photopolymerisation reactions of monomers/oligomers, which possesses environmental, economical, and production benefits. In this approach, photoinitiators and monomers/oligomers are two of the most important components of photopolymers for 3D printing. Specifically, photoinitiators absorb the irradiation light of a 3D printer and initiate the photopolymerisation reactions of monomers/oligomers layer-by-layer to produce the designed 3D objects, while monomers/oligomers can determine the final properties of the printed products. In this review, commercial photoinitiators and monomers/oligomers applicable for 3D printing are presented. Moreover, the newly developed photoinitiators and monomers/oligomers (from 2015 to 2017) for 3D printing of polymer-based materials with various properties and the application in 3D bio-printing are also demonstrated.