Two-dimensional (2D) nanomaterials have emerged as a cornerstone of modern materials science, owing to their exceptional physicochemical properties and versatility across various applications. Since the groundbreaking discovery of graphene, the family of 2D materials has expanded to include graphene, hexagonal boron nitride, 2D layered hydroxides, MXenes, perovskites, metal oxides, and graphitic carbon nitride, among others. Each class of 2D materials exhibits unique structural and functional attributes, enabling applications in electronics, energy storage, catalysis, sensing, and more. This chapter provides a comprehensive introduction to the diverse classes and structural variations of 2D materials. It explores how their intrinsic properties, such as electrical conductivity, optical responsiveness, magnetism, mechanical strength, and catalytic activity, are influenced by their atomic arrangement and thickness. By offering a systematic overview of the relationship between structure and properties, the chapter aims to illuminate the underlying principles that drive their functionality. The discussion concludes with an exploration of current challenges and a forward-looking perspective on the future of 2D materials. As the field advances, understanding these materials’ potential will be pivotal in unlocking innovative solutions for global technological and environmental challenges.