,  , Because communication facilitates behaviors that are critical for survival and reproduction, it is central to the study of behavior and evolution. One of the most important and difficult issues with respect to communication has been the definition of communication itself. Broadly, it can be defined as an exchange of information from a signaler to a receiver. However, evolution of a signal is likely possible only under conditions in which both the signaler and receiver increase fitness from the exchange of information, often referred to as “true communication.” The three primary sensory channels of communication used by animals are chemical, visual, and acoustic. Chemical signals are the oldest and most widespread method of communication. Visual and acoustic signals convey a great deal of information due to ease of modulation, flexibility of signal production, and fast transmission. The most widespread contexts in which animals communicate are sexual interaction and conflict resolution. Signals used for sexual interaction typically contain information about species identity and sexual attractiveness, whereas signals used for conflict resolution may contain information about resource holding potential. Other contexts under which animals communicate include territorial defense, parent-offspring interactions, social integration, sharing of environmental information, and auto-communication.