In the intricate world of modern engineering and technology, the silent battle against heat is constant and critical. From the powerful processors in data centers to the compact circuitry of consumer electronics, managing thermal output is paramount to ensuring performance, reliability, and longevity. As components become smaller, denser, and more powerful in a trend often referred to as Moore's Law, the challenge of heat dissipation intensifies dramatically. This has made thermal management not a peripheral concern, but a core discipline in design and system architecture. This chapter provides a foundational exploration of the diverse spectrum of cooling technologies, from foundational passive methods to cutting-edge emerging techniques. Leveraging over three decades of international expertise in mechanical, electrical, and plumbing systems, this guide aims to demystify these essential principles and systems, equipping the reader with a deep understanding of how we keep the future running cool.