This chapter focuses on how to most efficiently transfer and condition harvested energy and power with emphasis on the imposed requirements of microscale dimensions. The driving objective is to maximize operational life by reducing all relevant power losses. The chapter therefore briefly reviewes the electrical characteristics and needs of available harvesting sources and the operational implications of relevant conditioners. It then discusses the energy and power losses associated with transferring energy and useful schemes for maximizing system efficiency. It ends by presenting a sample microelectronic harvester circuit.