This book places a great deal of emphasis on providing practical solutions to thermal issues related to high power systems where liquid cooling is required. The book serves as a general thermal design guide for any liquid cooled systems with the main focus on microelectronic equipment that includes digital and/or analog devices. This book provides a comprehensive review and overview of all liquid cooling technologies as well as their applications to commercial products in industry. To facilitate design and analysis, the most commonly used correlations for the friction factor and heat transfer coefficient with either single phase liquid or two phase flow are summarized in the book. The general guidelines for thermal design of liquid cooled systems along with a step-by-step thermal analysis and design procedure are presented for liquid cooled systems with or without boiling. To meet the needs in telecommunication industry in which no liquid cooled rack is currently available commercially, a detailed system thermal design of liquid cooled telecommunication equipment is made, and two thermal design options based on open loop and closed loop cooling schemes, respectively are presented. Furthermore, the cooling solutions and design procedures discussed here can readily and easily be applied to any systems in other industries.