A maximum power point (MPP) tracking technique for electromagnetic energy harvesters is presented. The concept is based on using a bidirectional AC/DC converter to simultaneously counteract the effect of the output inductance and match the output resistance of the harvester, in order to perform maximum power transfer. The modulating signal for the AC/DC converter is generated by sensing and processing the output current of the harvester without requiring a priori knowledge of the value of the output inductance and output resistance of the harvester. The MPP is located by observing the change of the form factor of the differentiated output current under a perturb-and-observe method. A 12W prototype MPP tracker has been built and evaluated. The experimental results are favorably compared with theoretical predictions.