William Coffey has held research positions at the School of Theoretical Physics, Dublin Institute for Advanced Studies, and at the University of Salford. He was appointed Lecturer at the University of Dublin, Trinity College, in 1977, elected a Fellow of the College in 1981, and appointed a Professor of Engineering Sciences in 1985. Renowned for his work in the theory of Brownian motion and molecular diffusion Dr. Coffey has been the recipient of numerous honors, including Fellow of the American Physical Society, Member of the Royal Irish Academy, and Docteur Honoris causa (Université de Perpignan, France). Professor Coffey is the author of many books and more than one hundred and fifty papers. In particular, he is the coauthor of two previous Wiley books, Molecular dynamics (with M. W. Evans, G. J. Evans, and P. Grigolini) and Molecular Diffusion and Spectra (with M. W. Evans and P. Grigolini). Yuri Kalmykov is Professor of Physics at the University of Perpignan. Dr. Kalmykov has also been a Visiting Scientist at Trinity College, Dublin, and a Visiting Professor at Queen's University of Belfast, UK. The area of his research interests is non-equilibrium statistical mechanics, dielectric and Kerr-effect relaxation in gaseous and liquid dielectrics, magnetic relaxation of ferrofluids, relaxation processes in complex systems, etc. Dr. Kalmykov is a Fellow of the Institute of Physics, UK, and author of several books and over two hundred research articles that have appeared in numerous scientific journals including the Journal of Chemical Physics, the Physical Review (A, B, and E) and Physical Review Letters.