People can adjust their communication in a variety of ways for different contexts, audiences, and purposes. Although these adjustments often improve or facilitate interaction—that is, make it smoother, better, or easier—sometimes they do not. “Nonaccommodation” is a concept drawn from communication accommodation theory (CAT) and refers to adjustments in communication behavior associated with disaffiliation, expressing dissimilarity and/or obscuring information. Nonaccommodation can be defined and described in terms of either speakers’ or listeners’ experiences; it may also be intentional or unintentional on the part of a speaker. Researchers have studied nonaccommodation in terms of both its objective behavioral manifestations (e.g., linguistic divergence) and the subjective perceptions that relate to those behavioral manifestations (e.g., psychological divergence; over- and underaccommodation). Responding to nonaccommodation effectively can be challenging, and what constitutes the “best” or “most appropriate” response often depends on contextual factors and interactants’ goals. In line with the functions of accommodation described in CAT, nonaccommodation can influence communication effectiveness as well as the nature of interpersonal and intergroup relations. Generally, nonaccommodation hinders shared understanding and increases perceptions of social distance between individuals and their social groups. Often it is also associated with less positive evaluations of the people and groups involved, as well as lower levels of relational solidarity. Nonaccommodation occurs frequently across a wide variety of societally significant contexts, including intergenerational, medical/healthcare, police–civilian, family, and educational interactions. As such, it represents an important area for both theoretical and applied research.