Urea and thiourea form inclusion compounds in which organic and organometallic guest molecules are confined within non-intersecting, unidirectional tunnels within a solid urea or thiourea host structure. In this thesis, studies have been undertaken using a variety of techniques to examine the properties of urea and thiourea inclusion compounds, with a view to improving the understanding of the forces controlling the ordering of these systems on a molecular scale. From single crystal X-ray diffraction studies of urea inclusion compounds carried out at room temperature, different modes of ordering between guest molecules in adjacent tunnels, dependent on the guest species present, have been observed. Extension of these studies to low temperature, in conjunction with powder X-ray diffraction, has revealed information on phase transitions in both the host and guest substructures of urea inclusion compounds. Computer modelling, using a mathematical model developed for application to one-dimensional inclusion compounds, has been applied to model properties of n-alkane/urea and dimethylketone/urea inclusion compounds. The model has also been applied to the chlorocyclohexane/thiourea inclusion compound. EXAFS spectroscopy has been carried out on α,w-dibromoalkane/urea inclusion compounds to examine the local structural properties of the guest molecules. Halogenocyclohexane/thiourea and halogenocyclohexanes included within the pores of several zeolite-type hosts have also been investigated to determine the conformation of the guest molecules when constrained to occupy a confined environment. Additional studies have examined the potential for the polymerisation of monomeric guest molecules within the tunnels of the organic host structure of perhydrotriphenylene, and a solid state NMR investigation on the effect of magic angle spinning on the observed NMR spectrum for metallocenes.