The air/water interface and crystallisation have long been challenging to study despite their crucial importance in many areas of modern science. They can be difficult to study without interfering in some way with the process being observed and once the work it can be very challenging to interpret the results which have been gathered. This work attempts to understand the air/water interface and other air/solvent interfaces using variable angle spectroscopic ellipsometry. The values of the complex refractive index which are measured give insight into the nature of these interfaces and the apparent differences between water and other solvents. Work has also been performed to study the process of crystallisation through second harmonic imaging microscopy and single crystal x ray diffraction. To bridge these two areas, p-Nitrophenol has been studied in depth, with a literature review of the surrounding work on the compound, as well as studies on the effects of irradiation on the α crystal polymorph. Finally, the growth of a p-Nitrophenol layer at the air/water interface has been studied using Langmuir Blodgettry and tensiometry to understand the rate and mechanism of the growth.