There is currently a resurgence of interest in phase transitions in orientationally disordered molecular crystals. This is partly driven by the fact that new experimental and modelling tools now allow some of the open questions to be addressed properly for the first time, together with the need to understand the structural behaviour of molecular crystals for pharmaceutical applications. We are proposing to study the orientational ordering phase transition in para-terphenyl, C18H14, using total scattering with Reverse Monte Carlo analysis. This will enable us to address issues such as the determination of the orientational distribution function and the correlations between orientations of neighbouring molecules that drive the ordering phase transition.