The study of signal transduction mechanisms has become one of the most important branches of biomedical science, indispensable to understanding the normal actions of hormones, neurotransmitters and other extracellular signalling molecules as well as very many pathophysiological processes including inflammation and cancer. In this volume, the various techniques for measuring Ca2+ in the cytosol, in the various organelles and in the immediate surroundings of individual cells are described in practical details by experts, on the basis of their personal experience. Considering that the protein calmodulin is the main target for Ca2+ action in most cells types, a chapter on tracking calmodulin inside cells, using fluorescence technology, has also been included.