Second-person relations are relations between individuals knowingly engaged in interaction with one another. These are the social contexts within which it is appropriate for one to think of and address another as 'you'. This dissertation explores the practical consequences for agents of relating to others in this fashion. A critical analysis is offered of Stephen Darwall's theory of moral obligations in terms of demands that can be addressed from the perspective of a second-person. On the basis of the criticisms raised, a broader conception of 'second-personal reasons' is advanced according to which there are a variety of species of practical reasons that are essentially grounded in second-person relations between agents, besides moral obligations. A paradigm case of such a species is the reasons that are presented in requests, and one chapter of this work is devoted to explaining this power people often grant to others: to intentionally create new, discretionary reasons for them. Drawing from several historical antecedents - particularly Martin Buber, Simone Weil and Emmanuel Levinas - the analysis of second-personal reasons is extended to include a discussion of the proper object of agapic love, and a discussion of the possible significance that face-to-face encounters may have for moral epistemology.