This paper presents the first quantitative effort at determining the synergistic effects of organic compounds on the discharge, nucleation and growth mechanisms of electrodeposited tin phases at galvanostatically prepared polycrystalline copper electrodes. Cathodic and anodic transfer coefficients, exchange current densities and the rate constant for the discharge of tin(II) are presented. The discharge mechanism of tin(II) in the presence of all combinations of t-octylphenoxyethoxy ethanol, formaldehyde and phenyl-2-butenalimine remained a two step process with the transfer of the first electron being the rate-determining step. Furthermore, for additive combinations where nucleation occurred, hemispherical nucleation with three-dimensional (3D) growth was observed. This is accounted for by slow ion transfer across the cluster I electrolyte interface. The growth mechanism was found to change from instantaneous 3D growth to progressive 3D growth in the absence of t-octylphenoxyethoxy ethanol.