The present volume grew out of a NATO Advanced Study Institute held at Sogesta, Ita1y, during the summer of 1979. We are most gratefu1 for the generous financia1 support of NATO and for the provision of trave1 funds by The National Science Foundation (Washington, D.C., U.S.A.) and Ross Laboratories (Co1umbus, Ohio, U.S.A.). The Institute cou1d not have been held in a more suitab1e p1ace nor cou1d the staff at Sogesta have been more he1pfu1. The efforts of all concerned contributed to the success of this Insti- tute, Which was attended by 97 scientists from 23 countries. It is hoped the present vo1ume will be usefu1 to those who 'were unab1e to attend the Institute a1though it will be an incom- p1ete substitute for the Institute itse1f. Necessari1y, it lacks the formal and informal discussions that followed the lectures, the interchanges that occurred at group meetings, and, of course, the instruction given in the practicums. Neverthe1ess, we hope it will be useful to a wide range of professionals interested in growth and deve1opment. F. E. J. A. F. R.