Infrared v(OH) spectra of binary mixtures of methanol and acetonitrile have been studied over the whole concentration range. It has been shown that the overall band profile is influenced by a diverse range of hydrogen-bonded methanol aggregates (CH3OH)n with n extending to at least 4 along with at least two CH3OH/CH3CN molecular complexes (i.e. 1:1 and 2:1 CH3OH:CH3CN species). Band intensities and normalised concentrations of the various aggregates have been computed using a band fitting procedure and have been compared with the respective values expected from a multiple equilibrium model for complex formation. It is found that for the 1:1 complex behaviour it is essential to include the effects of the methanol n-mer network. It is emphasised that different perspectives on a given set of molecular interactions may be achieved by examination of both infrared and Raman spectra of the same system.