This book provides design-oriented models for the implementation of ultra-low-voltage energy harvesting converters, covering the modeling of building blocks such oscillators, rectifiers, charge pumps and inductor-based converters that can operate with very low supply voltages, typically under 100 mV. Analyses based on the diode and MOSFET models are included in the text to allow the operation of energy harvesters from voltages of the order of 100 mV or much less, with satisfactory power efficiency. The practical realization of different converters is also addressed, clarifying the design trade-offs of ultra-low voltage (ULV) circuits operating from few millivolts. Offers readers a state-of-the-art revision for ultra-low voltage (ULV) energy harvesting converters; Provides analog IC designers with proper models for the implementation of circuits and building blocks of energy harvesters, such as oscillators, rectifiers, and inductor-based converters, operating under ultra-low voltages; Addresses the design of energy harvesters operating from ultra-low voltages, enabling autonomous operation of connected devices driven by human energy; Demonstrates design and implementation of integrated ULV up-converters; Includes semiconductor modeling for ULV operation.