An understanding of the mechanisms by which plants perceive environmental cues, both physical and chemical, and transduce the signals that influence specific expression of genes, is an area of intensive scientific research. With the completion of the genome sequence of Arabidopsis it is understood now that a larger number of genes encode for proteins involved in signalling cascades and transcription factors. In this volume, different chapters deal with plant receptors, second messengers like calcium ions, phosphoinositides, salicylic acid and nitrous oxide, calcium binding proteins...