The rising popularity of the IoT and sensor net-works has risen the concern on how to power these devices. Bat-tery replacement is complex in large networks, in devices placed in harsh environments and in implanted biomedical devices. To tackle these limitations, energy harvesting and remote powering strategies have been proposed to recharge the device's batteries or even to allow battery-less devices. The use of piezoelectric transducers is interesting due to the large energy density, but several aspects make maximum energy extraction complex. In this article, the characteristics of piezoelectric transducers for energy extraction are analyzed and the most popular state-of-the-art solutions in the literature are reviewed.