The ever-growing electronic world has mandated the need to harvest energy in the current world. The total energy needed for these electronic and electrical systems is much more than we produce. This chapter explains the significance of harvesting energy by highlighting the applications that can be driven through the ubiquitous supply of energy. It also highlights a classification of technologies that are available for harvesting energy at macro levels. Three different types of energy harvesting techniques have been showcased, where each of the types has been elucidated in terms of their working mechanism, materials used to develop them and some of the targeted applications. The advantages and demerits associated with each of the shown technologies have also been mentioned in the paper.