The material in this book is derived from an Intensive Course in X-Ray Structure Analysis organised on behalf of the Chemical Crystallography Group of the British Crystallographic Association and held every two years since 1987. As with a crystal structure derived from X-ray diffraction data, the Course contents have been gradually refined over the years and reached a stage in 1999 where we considered they could be published, and hence made available to a far wider audience than can be accommodated on the Course itself. The authors were the principal lecturers on the Course in 1999 and have revised and expanded the material while converting the lecture notes into a book format. Any readers who participated in the 1999 Course will detect a number of changes, particularly in the inclusion of some material not covered in lectures, some updating and shift in balance, and differences of style made necessary by a non-interactive format.

Because of its origin, this book represents a snapshot of the Intensive Course, which continues to evolve, especially as the subject of chemical crystallography is currently undergoing more rapid changes than for many years, mainly due to the widespread availability of area detector technology and the exponential increase in computing power. Nevertheless, we believe it emphasises principles which will remain valid for a considerable time, and the particular application of those principles can be adapted to new developments for some time to come.

Since the book owes its origins to the Course, we wish to acknowledge our large debt to those who have dedicated much effort to the organisation of the Course since its inception; without them this book would never have existed, even as an idea. The first five Courses were held at the University of Aston, where the local organisers Phil Lowe and Carl Schwalbe set a gold standard of Course administration and smooth operation, establishing many of the enduring characteristics valued by participants ever since. Following the move to Trevelyan College at the University of Durham, Vanessa Hoy and then Claire Wilson have developed these firm foundations to even further heights of excellence. Throughout the Course’s history Judith Howard has provided overall guidance and expertise, particularly in fund-raising, and has spared the Course lecturers much concern with the practicalities of maintaining and promoting the Course. Several organisations, including the EPSRC, IUCr and commercial sponsors, have been long-standing and generous supporters of the Course.

Many colleagues have made contributions to the Course over the years, in lectures and in the crucial group tutorial sessions: a book format can never reflect the intensive interaction and lively atmosphere. These and the social aspects of the Course are probably at least as important in the memories of participants as the formal lecture presentations.

Most of all we are indebted to David Watkin.  The Course was his brainchild in the first place and he worked extremely hard to launch it and establish it as the enduring success that it has become. He gave up his involvement in the Course for a while, before it reached the stage of encapsulation in book form, but his influence is firmly stamped on the whole character of the Course and hence on this book. It is to him that we dedicate this work.

One aspect of the tutorial group sessions of the Course has been retained in modified form in the book. Most chapters include exercises, for which answers are provided in an appendix. Readers are encouraged to tackle the exercises at leisure and not consult the answers until they are satisfied with their own efforts. In the spirit of the tutorials, these exercises may also prove beneficial as a basis for group discussion.

In acting as overall editor for the conversion of the material from lecture notes to book format, Bill Clegg also wishes to thank the University of Canterbury, New Zealand, for the award of an Erskine Visiting Fellowship in 1999, during the tenure of which substantial amounts of the revision and editing were carried out.

Sandy Blake, University of Nottingham
Bill Clegg, University of Newcastle upon Tyne
Bob Gould, University of Edinburgh
Peter Main, University of York
June 2001