Multimodal behavior is the academic concept and research field concerned with the study of actions, interactions, or communication that simultaneously or sequentially employ and integrate information or expression across multiple distinct modalities. It investigates how agents, such as humans or artificial systems, utilize and coordinate diverse channels including verbal language, nonverbal cues, physiological signals, and physical actions to convey meaning, achieve goals, or interact with environments. Key characteristics involve the analysis of the dynamic interplay, synchronization, and synergistic effects arising from the combination of these modes, holding significance for understanding complex naturalistic interactions, developing sophisticated artificial agents, and designing effective human-computer interfaces.