This volume records the proceedings of a Forum attended by many leading researchers working in the field of Electron Density, Density Matrix and Density Functional Theory held at the Coseners' House, Abingdon-on-Thames, Oxfordshire, UK in early summer 2002. The meeting concluded with a Forum, ably chaired by B.T. Sutcliffe, in which the latest research and results were discussed. A record of this Forum is included in this volume. This book will be of value to researchers and research students in theoretical chemistry and theoretical physics whose work involves the theoretical study of atoms, molecules and the solid state. It will be of interest to quantum chemists and solid state physicists, to materials scientists and applied mathematicians.