An entrepreneurial firm's relationships with customers, suppliers, investors, universities, and other organizations have a significant and long-lasting impact on the survival and success of the firm. Yet, little research has focused on how the management of these relationships influences outcomes for entrepreneurial firms. This paper focuses on the customer relationships of new, technology-based firms (NTBFs). We aim to contribute to the literature on the governance of exchange relationships between NTBFs and their customers. Further, in so doing, we seek to explore the implications of such governance for the performance of new firms. Because of their small size, their "liabilities of newness," and their highly specialized, knowledge-intensive resources, NTBFs are able to maintain only a limited number of close customer relationships. Consequently, NTBFs often become highly dependent on one or a few of their customers. In this study, we focus on the relationships between NTBFs and their single largest customers. We refer to the customer that accounts for the highest proportion of an NTBF's total revenue as the "key customer." Strategic management literature, resource dependence theory, and transaction cost economics emphasize the risks associated with being dependent on an exchange relationship, focusing on the opportunistic use of power by the exchange partner. These perspectives suggest that firms can minimize their external dependencies and protect themselves against opportunism through the use of contracts. The present paper expands this view by also examining how flexibility in exchange governance may unlock potential benefits or dampen potential dangers that an NTBF faces in its commitment to its single largest customer, e.g., sharing the costs and risks of R&D with the customer, improving the reputation of the NTBF, and realizing savings in sales and marketing costs. We examine the extent to which the realization of the potential positive and negative outcomes of a high level of dependence are moderated by the flexibility of the exchange partners' attitudes toward contractual agreements. The research question that we seek to answer is: Does the manner in which a contractual agreement is implemented affect the outcomes of a customer relationship for an NTBF at high levels of exchange dependence on the key customer? We develop a set of hypotheses that examines how the governance of the key customer relationship affects the NTBF's new product development, reputation, and sales costs when exchange dependence on the key customer is high. We use the term "contractual governance flexibility" to refer to the extent to which the exchange partners are willing to adjust to changes in the relationship instead of relying on the contract. We test the hypotheses with survey data from 195 NTBFs in the UK. The results of regression analyses reveal that contractual governance flexibility moderates the relationship between exchange dependence and outcomes. In relationships with a high level of exchange dependence, greater contractual governance flexibility was associated with greater new product development and sales cost advantages. No such benefits were realized for relationships in which exchange partners relied heavily on the contract. These findings are important because they suggest that by relaxing formal contractual mechanisms governing a relationship, NTBFs can derive benefits from key customer relationships that are characterized by a high level of dependence. Our findings suggest that at high levels of exchange dependence on key customers, NTBFs can benefit when greater contractual governance flexibility is present. Our data indicated that, interestingly, NTBFs tend to do just the opposite: at higher levels of exchange dependence, NTBFs are inclined to rely increasingly on the contract. By so doing, they may fail to realize the potential benefits of the relationships, such as gaining access to complementary resources and reducing costs. These outcomes, which may be derived from dependent exchange relationships by means of contractual governance flexibility, can have a significant influence on the long-term development and competitive advantage of an entrepreneurial firm.