Liquid state physics no longer has the luxury status of an intellectual plaything – a kind of purgatory between gas and solid, a statistical mechanical jungle populated only by the foolhardy and/or academics. Pressing demands are increasingly being made upon the subject by adjacent branches of physics, and many people are being unwittingly drawn into the field from more conventional and immediately rewarding routes in physics. A subject which has not, as yet, satisfactorily accounted for the solid-fluid transition, nor which has yielded more than three further hard sphere virial coefficients in the 75 years since Boltzmann's original calculations, is evidently beset with problems: but there lies the source of the fascination.

This book is meant to be a guide to the uninitiated, and perhaps to broaden the outlook of those already there. It represents a very personal account of my own journey into the subject, and in consequence the content and approach might be considered in some respects somewhat idiosyncratic. I have made some attempt to present the material objectively, although inevitably one's own particular interests and viewpoints should and do assert themselves. Nonetheless, I felt the time was ripe to include separate chapters on the liquid surface and on the machine simulation methods, and to expand the by now routine statistical mechanical developments of the pair distribution associated with the names of Kirkwood, Born and coworkers, Bogolyubov, Percus and Yevick, and others. Of necessity some selection is inevitable, and I have arbitrarily restricted the discussion to the non-critical domain of the so-called ‘simple’ liquids, including the quantum liquids to a certain extent, although liquid water does receive a brief mention.