Violins are varnished to protect them against wear, from changes in relative humidity and to enhance the instrument's appearance. Furthermore, studies have shown that the application of varnish alters the mechanical and vibrational properties of the wood, respectively, the instrument. Commonly, the varnish impact has been studied by means of changes in stiffness, mass and damping properties of wooden test samples, and by changes in the modal parameters (i.e., eigenfrequency, eigenmode and damping) of top and bottom plates or the complete instrument, respectively. Although these properties determine the final sound quality, their changes have been less frequently studied than the chemical composition of the varnishes from historical instruments. This review focuses on the impact of varnishing on the vibro-mechanical properties of wood used for violins from material to complete instrument level, including the varnish properties and their influence on the moisture sorption. Based on a final discussion of the main impacts and results, an outlook specifies new avenues of research required to better understand the influence of varnish on wood used to make violins.