The main argument of this book is that cell signalling via nerves, hormones, local mediators and growth factors are not distinct phenomena, but branches of one general mechanism and should therefore be studied in an integrated manner. This volume is designed to act as a bridge between general texts and is aimed at biologists coming to the topic from a variety of backgrounds. The first two chapters introduce the general concepts of intracellular signalling and also cover the topic of direct cell-to-cell communication by cytoplasmic bridges (gap junctions). The remaining chapters cover the first and second messengers, starting with their structure, synthesis and release, progressing to the target cell and then working from the membrane inwards towards the nucleus. There is also a section on the mechanism of nervous conduction and the regulation of the ionic balace of cells. The final chapters discuss the regulation of cell growth and division and the special case of messengers acting via nuclear receptors.