Over the past decade, van der Waals heterostructures integrating two-dimensional materials (2DMs) with organic semiconductors (OSCs) have emerged as versatile platforms for next-generation electronic and optoelectronic technologies, combining the high mobility and mechanical robustness of inorganic layers with the chemical tunability and strong light absorption of organic materials. In these hybrid systems, interfacial exciton dynamics—including generation, diffusion, dissociation, and recombination—govern charge transfer, carrier transport, and ultimately device performance. Although enhanced responsivity, improved power conversion efficiencies, and low-voltage operation have been widely reported, a unified understanding of how excitonic processes dictate these gains remains incomplete. Variations in band alignment, dielectric screening, molecular orientation, and interfacial disorder critically modulate exciton binding energies and charge-separation efficiency, yet these effects are often considered independently. Here, we provide a comprehensive, exciton-centric review of 2DM/OSC heterostructures, spanning graphene, transition-metal dichalcogenides, and emerging 2D semiconductors that interface with small-molecule and polymer OSCs. By correlating experimental observations with theoretical modelling, we establish structure–property–performance relationships that clarify the role of interface engineering, molecular doping, and dielectric design in controlling excitonic behaviour. Representative device demonstrations—including ultrahigh-responsivity photodetectors, efficient hybrid photovoltaics, neuromorphic and memory elements, and emerging optospintronic systems—are critically evaluated. Finally, we outline challenges related to interfacial quality, reproducibility, and scalable fabrication, and highlight strategies such as controlled molecular assembly, passivation, and moiré exciton modulation to guide the rational design of high-performance hybrid optoelectronic devices.