Hall effect and resistivity measurements have been carried out as a function of hydrostatic pressure and temperature on a number of samples of indium phosphide ranging from exceptionally pure to highly doped. In the case of pure and lightly doped InP an iterative solution of the Boltzmann Equation has been used successfully to describe the temperature and pressure dependence of mobility over the helium temperature range. Measurements on the highest mobility samples of InP ever grown suggest that the conduction band deformation potential is 6. 7eV. For the case of highly doped material it was found that a theory of scattering from a correlated distribution of impurities describes both the temperature and pressure dependence of mobility well. Pressure dependent mobility measurements on a sample having an impurity density close to the Mott transition suggest that the inclusion of impurity band conduction in the analysis is necessary even at nitrogen temperatures and above. Such an analysis is used successfully to describe the temperature and pressure dependence of both mobility and Hall carrier concentration.