Intuition takes us only so far in understanding the particular obligations that states presume in reciprocity relationships. As a result, we know fairly little about who owes precisely what to whom, and on what schedule. Two polar patterns, specific and diffuse reciprocity, have been identified that answer these questions. Yet in some relationships, the parties do not expect one-for-one exchanges (the pattern that characterizes specific reciprocity) or exchanges very loosely matched in terms of both equivalence and value (the pattern that characterizes diffuse reciprocity). In this article, we develop a general explanation of the causes and consequences of reciprocal exchange. We argue that actors' expectations about time horizons and the degree to which they anticipate a reliable stream of benefits from a relationship drive their assumptions about the value and timing of trades, creating four distinct patterns of reciprocal exchange. This argument helps us understand how actors perceive their obligations, others' obligations, and thus, the content of cooperative and noncooperative behavior. Differentiating these types also allows us to infer what is likely to serve as effective bargaining leverage across situations. We use this argument to interpret the past three decades of Sino-American relations. While there is a large literature on this relationship, our argument illuminates the sources and consequences of various sets of expectations by each party over time.