Many of the electronic devices that are being designed nowadays are not expected to be powered constantly from the power grid. Wearables, remote controls, mobile phones, tablets, toys, cameras, etc. are supposed to have some type of energy supply that does not need a cord, at least during operation time. Devising such devices doesn’t have to be especially difficult, but several facts need to be taken into consideration to obtain a quality product. This book is intended to highlight the common problems that engineers face when creating such systems, explore alternative technologies, and present the tools to choose among them.