Techniques based upon the electrical response of the quartz crystal microbalance (QCM) have been widely used in laboratories as a routine tools. In this article we present and discuss applications of the QCM (or its variant, the electrochemical quartz crystal microbalance, EQCM) to the viscoelastic characterization of films. It is pointed out that correlations between the motion of quartz crystal and contacting films and overlayers as well as the influence of the electronic circuit on the electric state of the whole system are of fundamental importance in interpreting the results.