This book presents the study, design, modulation, optimization and implementation of low power, passive DT-ΣΔMs for use in audio applications. The high gain and bandwidth amplifier normally used for integration in ΣΔ modulation, is replaced by passive, switched-capacitor branches working under the Ultra Incomplete Settling (UIS) condition, leading to a reduction of the consumed power. The authors describe a design process that uses high level models and an optimization process based in genetic algorithms to achieve the desired performance. David Fouto is a researcher in the Department of Electrical Engineering, Faculdade de Ciências e Tecnologia of the Universidade Nova de Lisboa, Portugal. Nuno Paulino is a Professor in the Department of Electrical Engineering, Faculdade de Ciências e Tecnologia of the Universidade Nova de Lisboa, Portugal.