It has been a classical scientific cause to attempt to interrelate the response of an assembly of particles, large entities, molecules or atoms, in terms of their interparticle interaction characteristics. The interaction properties of, say, two particles is commonly referred to as an interaction law. The following reviews, briefly and in a personal manner, the way in which these laws may be currently established by direct experiment but concentrating primarily upon short range, or contact, interactions. No direct attempt is made to incorporate these laws into the description of the rheology of such assemblies. This latter problem is seen as a major and currently elusive limitation in the value, in this context, of direct interparticle studies for the a priori ultimate description of the properties of assemblies. The general supposition is that one day methods, most certainly numerical computations involving significant resources, will evolve to capitalize properly upon these data. A scheme for addressing the whole gambit of the interrelationship between interaction laws and the rheology of particle assemblies is introduced in Fig. 1.