This chapter introduces 3D System-on-Chip (SOC) technology, an advanced approach to semiconductor integration that stacks multiple chip layers to improve performance, power efficiency, and functionality. It explores the need for 3D SOCs, driven by the limitations of traditional 2D scaling and the growing demand for higher computing power in compact form factors. The advantages of 3D SOCs, such as reduced interconnect delays, lower power consumption, and increased bandwidth, are discussed alongside key design approaches like Through-Silicon Vias (TSVs) and Chiplet-based architectures. The chapter also examines the challenges of 3D SOC design, including thermal management, inter-layer communication, and manufacturing complexities. Finally, it covers EDA tools and methodologies that enable efficient 3D SOC design, addressing simulation, verification, and physical implementation in advanced semiconductor nodes.