The Second Winter School on the "~hysics of Finely Divided Matter" was held at the Centre de Physique des Houches from 25 March to 5 April 1985. This meeting brought together experts from the areas of gels and porous media. People with different backgrounds — chemists, physicists — from university as well as industrial labora- tories, had the opportunity to compare their most recent experimental and theoreti- cal results. Although the experimental situations and techniques may seem at first sight unrelated, the theoretical interpretations are very similar and may be divided roughly into two categories: percolation and aggregation. These are present for the description of the synthesis of some gels as well as for a description of the struc- ture of packings. They are also a precious help for understanding flows in porous media and hydrodynamic instabilities such as viscous fingering. A different aspect, still in its early stages, deals with the influence of a ran- dom medium on a phase transition. This leads to metastable states and is interpreted in terms of random fields. The following topics were covered: introduction to physical and chemical gels structure of packings and porous media microemulsions percol ati on aggregation elastic and dielectric properties of ill-connected media properties of gels near and far from the gelation threshold flow, diffusion and dispersion in porous media transitions in porous media. Most of these are rapidly growing subjects, and we hope that these proceedings will serve as a reference for those entering this fascinating area.