Abstract: In applications involving Resonant Vibration Energy Harvesters (RVEHs) the maximization of the extraction of power is of fundamental importance and a very crucial aspect of such a task is represented by the optimization of the mechanical resonance frequency. Mechanical Tuning Techniques (MTTs) are those techniques allowing the regulation of the value of RVEHs mechanical resonance frequency in order to make it coincident with the vibration frequency. A very great number of MTTs has been proposed in the literature, and in this presentation, the main of them are reviewed, classified and compared. In particular, the objective is to put in evidence the differences existing among the various MTTs, to compare their performance and to identify the open issues.