This comprehensive volume is a contribution to a new se ries initiated by the NATO Panel on "Gell to Gell Signals in Plants and Animals". The book reflects the outcome of an NATO work­ shop and bri ngs to mi nd two im portant questions: consideri ng the mass of relevant I iteratu reavai- able, is there any necessity for a new series of books - and considering the flood of compa­ rable meetings - is there any point in workshops of this nature and their publication? In order to deal with such questions adequately, much more space would be needed than is available in a foreword. Thus, the answers must remain rather superficial and, of course, rather subjective. To simplify the issue, the question of publication can be narrowed down to two fac­ tors - the financial risk, undertaken by the publisher, and the scientific risk, borne by the editor. If the book is good (with respect to lay-out and content) it will be a success - nothing will be lost­ the people involved will enhance their reputation! We are left with the question of the usefulness of workshops. Without doubt, it is indeed a useful procedure for experts to come together, in an atmosphere of harmony, and freedom from external pressures and time limitations, to discuss a well-defined theme. Wether in agreement or disagreement, a fair and open forum can be expectet for a variety of contributions.