During the past 20 years there have been amazing developments in low temperature physics, engineering, and biology. They form part of the very rapid post-war growth in pure and applied sciences of every kind. During this period several branches of biology including immunology, molecular biology and, of course, cryobiology, have split off from their parent disciplines. One result of this splintering has been the development of separate jargons used by the specialists and sometimes incomprehensible to those working in closely allied fields. The pure physicists, chemists, and the applied scientists, including physicians, surgeons, and pathologists, find the new jargons particularly baffling. We have attempted in this monograph to present to cryogenic engineers a picture of cryobiologists and their problems using as few strange technical words as possible. We hope that this book will help to bridge the gap which has already formed between them in spite of the opportunities for collaboration in many projects. We hope that it may also be useful to scientific research workers and postgraduate students of many kinds united only by curiosity about cryobiology. We are very much indebted to Dr. K. Mendelssohn, who insti­ gated us to produce a monograph and who reassured us that cryogenic engineers are as keen to understand the current trends in biology, and particularly in cryobiology, as we are to enlist their help. We have had much help in preparing this book.