Using microelectrochemical techniques, our laboratory has explored self-exchange-based electron transport in a variety of mixed-valent polymeric media. The transport rate is measured as the electron diffusion coefficient, D_e, or the self-exchange rate constant k_ex. The basic variables for electron transport in mixed-valent polymer materials include: (a) the physical mobility of the counterions of the polymer that migrate due to electroneutrality requirements, (b) the physical diffusion coefficient, D_phys, of the monomeric or polymeric oxidized and reduced molecular sites or ions relative to the rate of electron hopping or tunnelling between donor/acceptor pairs, (c) the observational timescale relative to these mobilities which provides the distinction between transient and steady-state experiments, and (d) the chemical environment of the polymer, whether dry and solvent-free or contacted by solvent vapour or liquid. Experimental strategies and results are presented for the measurement of rates of ion diffusion, D_i, in N₂-dry and solvent-wetted mixed valent polymers. In a dry, mixed-valent osmium complex polymer, the electron-transport rate measured under steady-state conditions, where no ion transport occurs concurrently, is much faster than the diffusion rate of the ion as estimated in a transient electrolysis experiment. In a solvent-wetted osmium complex polymer, the electron-transport rate measured under transient conditions is much slower than that of the ion which was measured under steady-state conditions. These circumstances allow isolation of individual processes and are interpreted as giving electron-transport rates not strongly influenced by macroscopic ion-transport rates. Cyclic voltammetry of [Co(bpy)₃]²⁺ and of Li⁺TCNQ^– in dry poly(ethylene oxide) polymer electrolyte solvents exhibits differing measured diffusion coefficients, D_app, for the oxidation vs. the reduction of each compound, reflecting the coupling of physical diffusion and electron self-exchange transport. Microdisc electrode voltammetry of solutions of a synthesized ferrocene mono-tagged poly(ethylene oxide) in a polymer solvent of comparable molecular weight gives D_app values smaller than those for ferrocene monomer dissolved in the same polymer solvent. The D_app in the former case measures the self-diffusion rate of a linear chain polymer within a linear chain polymer solvent. Measurability of this rate has implications for assumptions about diffusive mobility of redox molecules attached to polymer chains.