That plants can induce defences in response to damage has been well established and accepted by the scientific community. However, whether plants can assess that neighbours are damaged by herbivores or pathogens and subsequently induce defences has been received with skepticism for a long time. In recent years this topic has gained momentum as a result of many new data from laboratory and field experiments, involving in planta bioassays as well as detailed mechanistic analyses through analytical chemical and molecular biological methods. Therefore, we feel it is timely to devote for the first time a volume to the topic of plant-to-plant communication. In this special issue we bring together new studies that provide support for the transfer of chemical information between damaged and undamaged plants. This relates to intra- and interspecific signalling, to aerial as well as underground information transfer. The collective set of papers in this special issue shows that there is a rapidly growing pile of evidence in favour of plant-to-plant communication. The information presented should stimulate the study of this topic with respect to various aspects, such as elucidation of the mechanisms of information perception, elucidating the transcriptome changes of plant responses, investigating the ecological consequences of the responses of receiver plants, investigating the role of plant-to-plant communication in the evolution of plant defence, quantifying the effects under natural field conditions etc. Many colleagues were of great help in the realization of this special issue. We are grateful to the editor-in-chief of Biochemical Systematics and Ecology, Peter Waterman, for his enthusiastic support to our idea to edit this special issue. The invited authors have written the exciting contributions and have paid careful attention to be as critical as possible about the data. The following colleagues have helped us in reviewing the contributions: Ian Baldwin, Ted Farmer, Erkki Haukioja, Arne Janssen, Rick Karban, John Pickett, Wim van der Putten, Maurice Sabelis, Jack Schultz, Jennifer Thaler, Teja Tscharntke, Ted Turlings and Minus van Baalen. We thank all of the aforementioned colleagues for their enthusiastic support. We hope that this special issue will stimulate many others to join in this exciting research field so as to improve our understanding of the strategies that plants have to anticipate potential attack.