Laser flash photolysis has been used to obtain kinetic and mechanistic information for the reactions of substituted styrene radical cations with a variety of anions, alcohols, nitrogen-centred nucleophiles and alkenes. The reactions studied include nucleophilic addition to the P-position to give a substituted benzyl radical, electron transfer to regenerate the starting styrene, deprotonation of the radical cation for styrenes with a P-methyl group, and cycloaddition to give a cyclobutane or Diels-Alder product. The importance of steric and electronic factors, solvent, nucleophilicity, basicity and redox potentials in controlling the competition between the different reaction pathways is discussed.