<p>Physical activities are commonly associated with exertion. Yet most of the research to date has focused on the first-person, interoceptive questions of “What are the internal signals associated with exertion?” and “How well do subjective reports correlate with objective measures of energy expenditure?” Here we aim to broaden the scope of this research by asking “How closely are observations of exertion in other people correlated with first-person reports of exertion and objective measures of energy expenditure?” and “What factors influence the accuracy of exertion perception in others?” Although exertion often occurs in the company of other people, there is surprisingly little research on these questions. This is somewhat surprising, since the accurate perception of other people’s exertion is often critical, whether that be to cooperate with them, to compete with them, or to encourage them to go on. In this review, we first briefly review the large background on perceived exertion in oneself before turning to our central question of the perception of exertion in others. The small literature we review in the second section offers some clues about the potential exteroceptive signals available from individuals undergoing exertion. A third section in the review considers potential behavioral and neural mechanisms underlying the social perception of exertion, by considering the broader literature on action perception and social perception. In a final section, we offer suggestions for future research in this area, with the goal of including the perception of exertion as but one of the many facets of social perception more broadly.</p>