An interaction between two organisms in which information is conveyed from one to the other. Communication can occur between individuals of the same species (intraspecific communication) or between members of different species (interspecific communication). It generally involves the transmission of a signal from one organism to another; signals can be visual, chemical, or tactile or they can take the form of sounds. Visual signals between members of the same species are widely used by animals in such activities as defining and protecting territories and finding suitable mates (see courtship; display behaviour; bioluminescence). Chemical and tactile signals also play an important role in these activities (see pheromone). Social species rely heavily on all three types of signalling, the classic example being provided by the dance of the bees, in which information about the distance and direction of a food source is conveyed to other members of the colony. Visual signals, in the form of body coloration, are the principal means of communication between animals of different species (see mimicry; warning coloration). Sounds are more effective than visual signals for intraspecific communication over long distances and at night. Certain insects produce sounds by stridulation, while birdsong and language are sophisticated examples of sound signals in birds and humans, respectively.

Among plants, visual and chemical signals are important in communication. Flowering plants whose flowers are pollinated by insects or other animals depend on the colour, shape, and scent of their flowers to attract suitable pollinating agents. Some plants produce chemical signals to deter competitors and predators (see allelopathy), and certain volatile chemicals may induce defensive mechanisms in neighbouring plants. Trees can transmit chemical signals to their neighbours via the networks of hyphae produced by the mycorrhizal fungi associated with their roots.