Chalcogenide and chalcogenide-based nanomaterials are well known for its important applications. Chalcogenide nanostructures have attracted attention of researchers because of their narrow band gap energy, visible light harvesting ability, and various applications including solar energy utilization, visible-light-induced photocatalysis, visible light-assisted water splitting, optoelectronic devices, and removal of hazardous pollutants. This chapter covers the fundamentals and classifications of chalcogenide and chalcogenide-based nanomaterials. This chapter, in short, also discusses different types of sulfide, selenide, and telluride-based chalcogenides and of some their selected applications.