Building on the success of T.J.T. Spanos's previous book The Thermophysics of Porous Media, The Physics of Composite and Porous Media explains non-linear field theory that describes how physical processes occur in the earth. It describes physical processes associated with the interaction of the various phases at the macroscale (the scale at which continuum equations are established) and how these interactions give rise to additional physical processes at the megascale (the scale orders of magnitude larger at which a continuum description may once again be established). Details are also given on how experimental, numerical and theoretical work on this subject fits together. This book will be of interest to graduate students and academic researchers working on understanding the physical process in the earth, in addition to those working in the oil and hydrogeology industries.