Energy harvesting is the process by which energy is derived from external sources, e.g., solar power, thermal energy, wind energy, salinity gradients, and kinetic energy, and then stored for use by small, wireless autonomous devices, like those used in wearable electronics, condition monitoring, and wireless sensor networks. While energy harvesting is a promising path toward sustainable and self-sufficient power systems, it faces numerous significant hurdles that restrict its broad use. This book, The Challenges of Energy Harvesting, presents a comprehensive overview of fundamental harvesting techniques, design and material limitations, system integration issues, and future research prospects. This book is an essential resource for academics, engineers, and graduate students studying communications, embedded systems, and sensor networks.