The unique photoluminescence (PL) behaviors of polymers without extended π-conjugated structures have been attracting great attention owing to their versatile preparation methods and good processability for potential interdisciplinary application. Polymerization, as a chemical reaction, has been developed as an effective way to trigger photoluminescence, namely, polymerization-induced emission (PIE). Here, PIE is conceptualized as the process of transforming non-luminescent small molecules (i.e., monomers) into luminescent polymers or achieving redshifts in the emission wavelength during polymerization. It is proposed that the through-space interaction/conjugation of electron-rich moieties induced by diversified inter/intra-chain interactions trigger PIE. In this chapter, recent advances in PIE luminogens (PIEgens) are summarized, involving in chemical structures of PIEgens, polymerization methodologies, and the principle of PIE effect. Further investigation on typical examples for understanding the relationship between structures of polymers and PL properties helps to elaborate the basic design principles of high-efficiency, color-tunable (blue to near-infrared) PIEgens for potential applications. Moreover, the challenges and perspectives in this area are also presented.