This 12th edition of The Maudsley Prescribing Guidelines in Psychiatry marks its 20th year in continuous production. Readers who have owned or used previous editions will find this edition no different in style from previous incarnations. This is deliberate—the feedback we receive suggests the organisation and structure are well liked. Each section of The Guidelines is a densely referenced but succinct review of the literature, set along-side some fairly broad recommendations for practice. Each of these sections has been updated and revised, and some new ones added (for example, interpreting clozapine plasma levels, post-mortem plasma levels, summary of depot pharmacokinetics). Much of the guidance provided in this edition has changed as a result of more recent research; some of it to a small extent, some of it to an extent amounting to a reversal of prior guidance (for example, on the use of fish oils in psychosis). These changes reflect the very nature of the scientific method—that hypotheses come and go as evidence mounts or is countered.

This edition of The Guidelines has a particularly international flavour. This is because the 11th edition sold more copies outside the UK than in it, and because there are, we think, at least ten translations of The Guidelines in existence. Although The Guidelines are still essentially our local guide to prescribing, we have made a special effort to widen, geographically speaking, its utility. This is most noticeable in the inclusion of drugs not licensed in the UK (e.g. ziprasidone, iloperidone, desvenlafaxine), but widely used in other countries. Readers should, therefore, not assume that every drug mentioned in The Guidelines is available in their own country. The reader should also be aware that no guideline could take account of every psychotropic drug used around the world, so omissions are inevitable.

As with previous editions, very special thanks are due to Maria O'Hagan who manages the writing and structuring of The Guidelines; an increasingly complex process given the size, complexity and heavily referenced nature of the current edition. Thanks are also due to the many expert contributors to The Guidelines who are listed overleaf, and to Adam Gilbert, our editor at Wiley.

David Taylor