Rapid advances have been made in the properties of metastructures, including phononic crystals, metamaterials, and metasurfaces, with respect to their robustness, high power density, and broadband behavior. This presents unique advantages for energy harvesting devices to meet the demands for technology upgrades in various applied science and engineering applications such as wireless sensors, MEMS, and wearable devices. We provide a systematic overview of the mechanisms underlying the above properties, considering different configurations of wave localization in elastic metastructures for energy harvesting purposes. The energy localization can result from cavity modes, topologically protected edge/cavity modes, chiral edge mode, focusing effects, among others. Finally, we give the prospects of energy harvesting metastructures such as the introduction of nonlinear design, time-modulation, machine learning inverse design, and nonlocal effects.