Granular matter serves as a prototype of collective systems far from equilibrium and can be used to exemplify many concepts now associated with nonlinear dynamics and complex systems: Self-organization, invariance and symmetry breaking, various forms of pattern formation-ranging from waves to chaos to coarsening-networks, and hysteresis. The foundational concepts apply across a wide range of scales-from fine particles to ice floes-and across a wide range of technological fields. It serves also as a test-ground and illustration of the benefits and drawbacks of discrete and continuum viewpoints. However, in spite of being an integral part of the origins of chemical engineering and a topic of unquestionable practical importance, granular matter as a sub-discipline was not a central part of the basic tool-kit that launched the modern version of chemical engineering back in the 1960s. It should have been. One can only speculate how the course of ChE would have been altered if this had happened. (c) 2005 Elsevier Ltd. All rights reserved.