We firmly believe that a book of this nature would lose its style and consistency if it was the product of multiple authors with different specializations However, one consequence of this decision is that we have had to review a great deal of work outside our own fi elds of specialization This has meant many pleasant, but demanding, months buried in the literature, and we wish to thank our Universities Carleton and Liverpool John Moores-for granting each of us our fi rst-ever sabbatical to devote time to the development of the book We began writing this book over 2 years ago, but without the support of our home institutions, it would have taken a whole lot longer Our collaborative research has also benefi ted from several grants from The Royal Society of London, to fund visits by Dave Wilkinson to Ottawa