Since the publication of my previous monograph in 1974, important progress has been made in the broad area of calcium research, partic- ularly as it pertains to secretory phenomena. The significant advance in methodology, while widening the scope of our knowledge, has caused research in this particular area to become more and more specialized. It has, therefore, become increasingly difficult for researchers to consider and evaluate work outside their own areas of specialization and to com- prehend the field from a broad perspective. While many valuable re- views on the importance of calcium in cellular function are being pro- duced, they have not attempted to pull together all of the existing knowledge into a more general narrative. This volume brings together experimental data and theories from diverse sources, and attempts to synthesize into a broad conceptual framework the massive amount of specialized information that presently exists in the general area of cal- cium metabolism and the secretory process. It is impossible in a book of this length to discuss specific references in detail and still maintain readability, so generalizations must be made.