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.