This book, printed by WHO, is meant to serve as a guide for the development of Primary Health Worker systems in communities all over the world. The book should be adapted to the particular needs and conditions of the community that will benefit from its use. Included are descriptions of the structure and content of training for the primary health worker on the basis of the most common health problems found in the communities of developing countries. Divided into three parts, Part I is intended for use by the primary health worker as a text and a guide for his/her work. Part II should be used by the health worker's teachers, tutors and supervisors and Part III discusses the adaptation of the book to local conditions