This paper describes the use of electrochemical quartz crystal microbalance (EQCM) and crystal impedance methods to study mobile species and polymer dynamics in electroactive polyvinylferrocene and polybithiophene films. For rigidly coupled films, the EQCM is a simple gravimetric mobile species population probe. Individual mobile species contributions can be separated by transient experiments. For non-rigid films, the EQCM responds to both mobile species transfers and film viscoelastic changes; these can be distinguished by the crystal impedance method. Slow polymer structural changes can lead to EQCM responses that depend upon film history and experimental time scale. A multi-dimensional extension of the scheme-of-squares can be used to rationalize these effects and to visualize mechanistic pathways.