In response to the pressing global energy crisis and environmental pollution, recent years have witnessed a surge in research on semiconductor photocatalytic technology. This innovative approach utilizes light energy to catalyse chemical reactions, holding promise in addressing both energy scarcity and environmental degradation. When exposed to visible light, these materials initiate electron–hole (e−/h+) pairs, which serve as agents to split water into hydrogen and oxygen and to effectively eliminate a broad spectrum of industrial, pharmaceutical and agricultural pollutants that are detrimental to our environment. Among the semiconductor nanomaterials, metal chalcogenide-based photocatalysts have emerged as standout performers, exhibiting exceptional efficiency in solar energy induced fuel generation and environmental remediation. This chapter presents, in a nutshell, the recent advancements in designing and synthesizing metal chalcogenides, with a specific focus on extensively studied CdS nanocrystals and their composites. It aims to provide an overview of the fundamental properties of these compounds and commences with an introduction to photocatalytic reactions, offering a historical perspective on the evolution of this pioneering field. The chapter comprehensively explores the application of metal chalcogenides as photocatalysts for diverse purposes, ranging from hydrogen production to carbon dioxide reduction and the degradation of various pollutants. It meticulously details their catalytic potential in driving these crucial reactions forward. Concluding with a visionary outlook, the chapter discusses future possibilities for leveraging chalcogenides as photocatalysts and elucidates the potential of chalcogenide-based heterostructures. This exploration not only encapsulates the modern trend in photocatalyst research, but also illuminates the promising pathways towards sustainable energy generation and environmental rejuvenation.