Abstract <p>This review aims to provide a comprehensive overview of photopolymers for additive manufacturing (AM) applications, with particular attention to the 3D printing (3DP) processes for thermosetting polymeric materials and the main mechanisms and reactions involved during their photopolymerization process. The introduction highlights the principles and significance of photopolymerization in AM. It is followed by an exploration of free-radical (FRP) and cationic photopolymerization (CP), the two main mechanisms underpinning these processes. The focus then shifts to the AM technologies suitable for photopolymer processing. Photopolymer-based AM technologies, such as vat photopolymerization (VPP) and ink-jet (IJ) photopolymerization, are examined in detail. VPP has been widely studied for its ability to produce 3D-printed components with highly complex geometries and good final resolution by selectively curing liquid resin in a vat through targeted light-activated polymerization reactions. Similarly, IJ, which involves depositing droplets of photocurable resins in a controlled manner and curing them with light, offers precise material deposition, enabling the creation of more detailed and intricate structures. Finally, the review addresses the shift from monomers derived from fossil-based sources to those coming from bio-sources. This transition is driven by the harmful effects of using polymers derived from non-renewable resources and the increasing emphasis on sustainable development. Research and development efforts aimed to use bio-based precursors are discussed in this context. The conclusions and outlook summarize the findings and offer perspectives on future research directions in photopolymerization for AM, emphasizing innovations in bio-based precursors and advancements in AM technologies.</p> Graphical abstract <p></p>