This unique book has an exciting story to tell about Ca2+, the versatile Master Cell Signaler whose influence reaches into all corners of the cell and controls cell proliferation, differentiation, cell functions too numerous to list here, and even cell death. The book begins nearly 4 billion years ago with the emergence of life on the newborn Earth. One of the great turning points in the history of life on Earth, The Great Ca2+-Driven Eukaryotic Revolution, happened about 2 billion years later when Ca2+ was converted from a dangerous killer that had to be kept out of cells into the versatile Grand Master of cell signalers. It was this revolutionary conversion that enabled the development of eukaryotic cells from which came animals with shells, internal and external skeletons, muscles and brains, and, of course, the plants. The reader will be taken on a tour of tissues chosen to best show three (proliferator, differentiator, killer) of Ca2+’s many faces.