The topic of sub-threshold VLSI has been discussed since the 1970s when the minimum supply voltage was theorized based on various sub-threshold models. It has been used in simple designs, such as watches and hearing aids. In new and upcoming wireless applications, such as distributed microsensors or medical applications, minimizing energy dissipation is the primary concern and has motivated investigation of the optimum design for minimizing energy dissipation or power for a given performance constraint. Sub-threshold circuits are ideal for this class of applications, thus making sub-threshold VLSI a realistic solution. This book combines the research of two MIT graduate students, which has spawned an exciting new field of research into sub-threshold circuit and system design. The work includes the research of Alice Wang who designed the first 180mV sub-threshold processor that minimizes energy dissipation and Benton Calhoun who has worked on modeling the optimum voltage to minimize energy dissipation and has designed a sub-threshold SRAM. The book includes a survey of the field of sub-threshold and low-voltage design and will delve into various aspects of sub-threshold circuit design such as modeling, logic and memory circuit design. One important chapter of the book is dedicated to optimizing energy dissipation which is a key metric for energy constrained designs. This book also includes invited chapters about the subject of analog sub-threshold circuits.