The ability of plants to exchange RNA molecules and transcription factors between cells and tissues is a relatively recent discovery. However, all areas of research such as plant development, metabolism, and plant pathogen interactions now realize the importance of this phenomenon. In this book, experts from the field of intercellular transport deal with various aspects on intercellular transport of viruses and plant endogenous macromolecules such as transcription factors, small silencing-induced and micro RNAs, and other RNAs and their function as signals. The aim of the book is to provide the basic information on the cell-to-cell transport mechanism and to give an overview of the current knowledge of this relatively new field of research. To quote the words of W.J. Lucas pioneering discoveries in this field of cell-to-cell and long-distance signaling should certainly entice talented young scholars to join this frontier area of plant biology . He is certainly right as we got only a first glimpse on the cellular factors regulating intercellular transport and the functional diversity of the ever-increasing number of proteins and RNA molecules found to move between cells.