This book is the first one written about the JAK/STAT pathway. The JAK (Janus Kinase) Protein tyrosine kinases are novel phosphotransferases absolutely required for cellular signalling downstream of non-catalytic cytokine receptors (amongst others). These molecules are components in pathways utilising the STAT (Signal Transducers and Activators of Transcription) transcription factors. The basic components of the JAK/STAT pathway are covered in detail, and the centre piece of the book is a guided tour of the pathway itself. An interesting addition to the book is the chapter on the use of Drosophila melanogaster as a genetic system to probe the pathway at the whole organism level. The book is targeted to researchers who have an interest in intracellular signalling.