Calcium is arguably the most diverse and widespread of the intra-cellular second messengers, being involved in many mechanisms of cellular biochemistry, physiology and pathology, where it plays a key role in signal transduction. Hormones and other extra-cellular agents bring about many of their effects by causing changes in intra-cellular calcium concentration. This book provides a comprehensive description of current techniques for measuring intra-cellular calcium concentrations, including protocols for the use of fluorescent, bioluminescent and metallochromic indicators, and various other intra-cellular probes. Also outlined are methods for controlling and changing the calcium ion concentration in cells, as well as procedures used to study the important proteins involved in the membrane transport and intra-cellular binding of calcium.