Calcium signalling is an astonishing example how a simple caption can trigger and regulate an enormous variety of cellular and physiological responses. Ca2+-signalling routes very often involve Ca2+-binding proteins that sense changes in intracellular [Ca2+] and trigger cellular responses by regulating specific targets. One fascinating group among these Ca2+-sensors are the neuronal calcium sensor (NCS) proteins, named for their localisation in neuronal tissue (although there are reports of their expression in non-neuronal tissues as well). While recent excellent reviews have covered key aspects of this protein group, the field expanded in recent years making it more and more difficult to represent every facet of this ongoing research endeavour. This book is intended to represent properties of NCS proteins.