Across the complexity of molecular systems, which have now been studied in great detail at well-defined, single crystal surfaces, particularly metal surfaces, there is a great variety in the strength, nature and significance of the interamolecular interactions which are possible. It is the balance of these interactions with the adsorbate/substrate interaction that is a key determinant of the two dimensional order, which can be achieved in the system. In the simplest cases, the interaction may be limited to Van der Waals' attractions balanced by local steric repulsion, while in more complex cases, highly directional H-bonding interactions can dominate the interadsorbate interaction. In the case of adsorption on relatively soft metals such as copper, silver and gold the strength of the interaction of the molecule with the surface atoms can be comparable with or even greater than that between the surface metal atoms, this can lead to the formation of highly ordered 2D adsorbate structures involving significant translocation of metal atoms, most likely in the form of metal adsorbate complexes, and consequential large scale restructuring of the surface. In this presentation, some examples of the relevance of intermolecular interactions in determining adsorbate structures in the sub-monolayer to monolayer regime will be given based on our studies of molecules ranging from aromatic hydrocarbons, through alkane and fluoroalkane thiols to simple biomolecules, such as amino acids and nucleic acid bases. In a somewhat more detailed description of two adsorbate-substrate systems, the role of a two dimensional monolayer in templating a novel three dimensional bulk structure will be described and, in the other example, the ability of a racemic mixture of adsorbing molecules to exploit intermolecular interactions leading to chiral phase segregation will be demonstrated.