Scholars across domains in psychology, physiology, and neuroscience have long been interested in the study of shared physiological experiences between people. Recent technological and analytic advances allow researchers to examine new questions about how shared physiological experiences come about. Yet, comprehensive guides that address the theoretical, methodological, and analytic components of studying these processes are lacking. The goal of this paper is to provide such a guide. We begin by addressing basic theoretical issues in the study of shared physiological states by presenting five guiding theoretical principles for making psychological inferences from physiological influence-the extent to which one dyad member's physiology predicts the other dyad member's physiology at a future time point. Second, keeping theoretical and conceptual concerns at the forefront, we outline considerations and recommendations for designing, implementing, and analyzing dyadic psychophysiological studies. In so doing, we discuss the different types of physiological measures one could use to address different theoretical questions. Third, we provide three illustrative examples in which we estimate physiological influence, using the stability and influence model. We conclude by providing detail about power analyses for the model and by comparing the strengths and limitations of this model to pre-existing models. Scholars have utilized physiological approaches to capture psychological experiences of individuals-including emotions, motivations, and attention-since the early 20 th Century (e.g., Cohen & Patterson, 1937;Darrow, 1929;Jacobson, 1930; Mittleman & Wolff, 1929). For example, early work by Carl Jung examined electrodermal activity as a measure of attention to different stimuli in healthy and clinical samples (Ricksher & Jung, 1908). Beginning in the 1950s, social scientists started to collect data from two or more people in interpersonal interactions to measure interdependence between their physiological states. Early work focused on how similarity between patients' and therapists' heart rates mapped onto behavioral processes such as rapport and antagonism (Coleman, Greenblatt, & Soloman, 1956;DiMascio, Boyd, & Greenblatt, 1957). Since that time, physiological influence has been used to study romantic couples, parent-child dyads, and newly-acquainted dyads and teams, and influence has been associated with relationship quality, individual differences like attachment, and the development of self-regulation and trust (Hill-Soderlund et al., 2008;Levenson & Gottman, 1983;Mitkidis, McGraw, Roepstorff, & Wallot, 2015;Suveg, Shaffer, & Davis, 2016; for reviews see Timmons, Margolin, & Saxbe, 2015;Palumbo et al., 2016).A primary strength of studying physiological influence in interpersonal encounters is that it allows scholars to test theoretical questions that are not testable using traditional measures of self-report or behavioral recordings alone. For example, physiological measures can provide continuous information ...