As of 2013, the number of mobile electronic devices has surpassed the number of humans on the planet. Interminable mobility and the need to stay connected have necessitated the development of mobile and uninterrupted power sources for these devices. Whereas the power requirements and size of microelectronic devices have shrunk drastically, the corresponding improvement in energy storage technology has been disproportionate. Many real-world applications demand a self-contained power source that needs minimum maintenance and that can generate energy for long, indefinite periods. Ambient energy, which is abundant in nature and in human activity, has the potential to be an infinite and renewable energy source. Owing to rapid advances in technology, it is now possible to convert ambient energy into electrical energy, which finds use in numerous fields such as defense, aerospace, structural health monitoring, environmental monitoring, wildlife monitoring, medical diagnosis, and healthcare. Ambient energy harvesting has the potential to replace conventional sources, which are limited and adversely affect the environment, and facilitate clean, green, and sustainable energy for all.