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.

It has long been recognized that "All the necessary information required for the energy and for calculating the properties of molecules is embodied in the first- and second-order density matrices". The wave function contains much more information than is required to yield the energy or other property. But the density matrices must correspond to some physically acceptable wave function. Coleman, one of the distinguished participants in the Forum, has dubbed this "Coulson's challenge". His paper describing recent work on the N-representability problem is included in this volume. McWeeny discusses some unsolved problems in density matrix theory and density functional theory; and Bader discusses the use of the electron density in explaining the structure and properties of atoms and molecules.

Density Functional Theory is widely used in studies of molecular and solid state systems. Yet the theoretical apparatus for this approach remains under active development. Theophilou describes a new formulation of density functional theory. Gross and his coworkers present a time-dependent theory for molecules in strong laser pulses. Nagy considers pair density functional theory, while Ludena and his colleagues examine functional N-representability in density matrix and density functional theory.

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.