The volume of research into the roles of ROS in plants is currently growing. Thus, the purpose of this book is to present recent advances in this field. The constitutive chapters are mainly arranged around four topics: (1) the generation of ROS, their network signalling, including the retrograde signalling from the chloroplast to the nucleus and the cross-talk with hormone signaling, (2) the signaling role of ROS produced in some sub-cellular compartments, (3) the role of ROS in plant growth, development, functioning and stress acclimation, and (4) their role in biotic and abiotic interactions. In thanking the authors for their contributions, we are convinced that the forthcoming years will bring new exciting insights into this field. Unravelling the sensing and transduction of ROS, including the post-translational regulation, the modulation of their concentration at subcellular level, and the interaction networks with the reactive nitrogen species, as well as their possible role in epigenetic processes, will shed new light on ROS action in plants.