"The calcium ion has an unusual importance in biological phenomena, and the literature concerning its effects is extremely voluminous." That this statement, written more than 30 years ago (1), also describes the situation today was certainly expected if not anticipated by L. V. Heilbrunn, whose text on general physiology highlights the then known numerous and critical roles performed by calcium in living organisms. While progress has surged, we have yet, regardless of appearances, to reach an "Age of Calcium," wherein calcium might be a physiologist's equivalent of DNA. Even so, there have been remarkable advances in detailing many of the molecular processes by which calcium exerts its variety of effects. This year's Cell and Membrane Physiology section surveys not only permeability mechanisms by which the cellular level of calcium is regulated ,but also some of the actions that calcium has in modifying membrane properties and in modulat­ ing cellular functions. Of the following articles, each in its own way empha­ sizes current aspects and some of the exciting developments that are taking place in the field. While the coverage could not possibly be comprehensive, we hope that in future years this area will be updated as well as expanded.