Pi-conjugated polymers (PCPs) are organic macromolecular systems characterized by backbone chains with alternating single and double bonds and are fascinating materials for energy-related applications. The first chapter shall help those readers who are new to the domain of PCPs to assimilate the fundamental features and the excellent opportunities associated with such macrosystems. Chapter 2 focuses on a special and growing class of PCPs -- heavy main group element containing heterocyclic systems and their unique properties. The dynamic domain of conjugated porous polymers, versatile photocatalysts, is discussed in Chapter 3. The synthetic strategies, functional modifications, characteristics, and recent applications of poly(oxadiazole)s and poly(indolocarbazole)s have been presented in Chapter 4. A basic understanding of the photophysics of conjugated polymer nanoparticles and the related fabrication routes are illustrated in Chapter 5, followed by the illustration of the theory behind the utilization for modelling and simulation in Chapter 6.