This chapter explores the intricate components and processes of the geosphere, the Earth’s solid foundation, and its profound influence on the globe. Beginning with an overview of the geosphere’s layers—crust, mantle, and core—this chapter highlights their composition, formation, and dynamic interactions. The geothermal gradient is discussed, emphasizing the role of internal heat in shaping geological phenomena. The lithosphere, as a rigid outer shell, is examined in detail, focusing on its tectonic activity and the movement of plates atop the more ductile asthenosphere. A detailed analysis of tectonic plates covers their types, interactions, and boundaries, shedding light on processes such as subduction, rifting, and lateral sliding. These interactions are the primary drivers of earthquakes, volcano formation, and mountain building. Earthquakes, resulting from sudden energy release along fault lines, are presented as a direct consequence of tectonic stress. This chapter concludes with an exploration of convergent boundaries and volcanic activity, showcasing the dynamic interplay between Earth’s interior and surface. This chapter comprehensively overviews the geosphere’s structure, processes, and profound influence on Earth’s surface and ecosystems.