Human–animal interaction (HAI) research has expanded across therapeutic, educational, and applied domains, yet it continues to rely on relational constructs, such as bonding, attunement, and presence, that lack consistent operational definition. Advances in dyadic synchrony research have provided measurable evidence of physiological and behavioral alignment across interacting systems, including in cross-species contexts (Beetz et al., 2012; Callara et al., 2024). However, synchrony alone does not account for the broader regulatory organization observed in sustained HAI relationships or socially structured animal groups. This conceptual article proposes relational coherence as a graded, multi-level regulatory construct integrating autonomic, behavioral, attentional, and network processes. Drawing on social regulation theory, coordination dynamics, joint attention research, and animal social network studies (Farine & Strandburg-Peshkin, 2021), relational coherence is defined as cross-level regulatory integration that contributes to patterned interactional stability. The construct is explicitly differentiated from dyadic synchrony and bounded to avoid therapeutic or metaphysical overextension. Methodological implications for multi-channel measurement and network modeling are discussed. The framework aims to clarify relational processes in HAI while remaining empirically grounded and theoretically disciplined. Keywords: human–animal interaction, relational coherence, dyadic synchrony, co-regulation, coordination dynamics, social regulation