Management of an entire portfolio of customers who are at different relationship stages requires a dynamic theory of exchange relationships that captures the trade-offs between scale economies and lifetime customer value. This article contributes to the understanding of relationship management by developing a typology of exchange relationship mechanisms and a model of relationship dynamics and by simulating the model to provide guidelines for customer portfolio management. An important insight from the research is that a key to the creation of value through closer relationships lies in bringing weaker relationships into a portfolio in the first place. Another insight is that firms that position themselves toward offerings with low economies of scale, such as personal services, must build closer relationships to create value.