It could be said that this book was conceived in December 1975 in Göteborg, Sweden, where Göran Sällfors had invited Peter Wroth and myself to Chalmers Tekniska Högskola to give a five-day course on Critical State Soil Mechanics. It was felt then that the material presented in that course ought to become a book. As the years passed outlines for such a book were sketched, but progress was slow in spite of good intentions. The eventual stimulus for labour to begin in earnest was provided in February 1985 by Yudhbir, who organised the Workshop on Critical State Models and Behaviour of Soils at the Indian Institute of Technology, Kanpur, as part of their Silver Jubilee celebrations. This book took shape in the course of discussions with Hideki Ohta in our smoke-filled room at Kanpur.

Since Peter Wroth and I (together or separately) had given many courses of lectures on Critical State Soil Mechanics, much of the material in this book has been aired previously in some form or other. I have endeavoured to give due acknowledgement for those ideas for which I cannot claim originality. Those who have attended any of these courses will discover that the sequence adopted here is quite different from that of the courses. The first lectures of the courses were devoted to the notion of critical states for soils (the latter part of Chapter 6), followed by simple applications of critical state lines to estimation of undrained strengths (early part of Chapter 7) and interpretation of index tests (Chapter 9).