Animal communication serves a wide range of functions, such as defending territories and attracting mates. Producing the appropriate signals for each social encounter is essential, but how communication behaviors are selected and adjusted in a context-dependent manner is poorly understood. This question can be addressed on many levels, including sensory processing by peripheral organs and the CNS, sensorimotor integration in decision-making brain regions, and motor circuit activation and modulation. Because neuromodulator systems are able to adjust outcomes at each of these levels, they are a useful lens through which to explore the mechanisms underlying complex patterns of communication. It has been clear for several decades that understanding the logic of input-output decision making by the nervous system requires much more than simply identifying the connections that link sensory organs to motor circuits; this is due in part to the fact that neuromodulators can promote distinct and temporally dynamic responses to similar signals. The role of neuromodulators in regulating motor output of central pattern generators is well established, however, combinatorial actions of multiple neuromodulatory substances are often overlooked. We review the complex roles of neuromodulators in diverse behaviors with the goal of applying those lessons to the study of communication. We argue that identifying the full suite of neuromodulators involved in regulating behavioral circuits at any level of control, from sensory organs to motor circuits, may be a necessary first step toward a fine-scale understanding of how behavioral context elicits appropriate communication signals.