This book addresses diverse aspects of signaling at all levels of plant organization, starting from single molecules; through vesicle recycling and organelles, dynamic actin cytoskeletons, and plant organs bending in response to sensory stimuli induced by abiotic cues such as gravity and light; up to the whole organism as related to its circadian clock or pathogen defense. Emphasis is placed on the integrative aspects of signaling, which foster our understanding of sensory and communicative plants in all their complexity.