Significant advancements in thermal management technologies have been made in recent years for defense, commercial, and space systems. This volume summarizes important progress in addressing challenges for electronics cooling ranging from near the junction of the device to the system level. This chapter provides an introduction and overview of this volume. The first chapter examines GaN composite substrates for near junction thermal management of high power, wide band gap power amplifiers. The next chapter discusses opportunities in nanostructured thermal interface materials. The following chapter presents recent developments in thermal ground planes as heat spreaders. The subsequent four chapters focus on active cooling approaches including one on single-phase liquid flow, one for three-dimensional integrated circuits, one on flow control of two-phase microchannel cooling systems, and one on thermo-electrics for hotspot cooling. The last chapter discusses thermal management in LED packaging.