In the psychotherapy literature, outcome expectation (OE) is pantheoretically defined as one’s prognostic belief about how much a forthcoming or in-progress treatment will help. Although commonly considered a patient variable that, when positive, can help facilitate improvement, there is growing recognition that this expectation type occurs in a relational context. That is, therapists also have expectations about their patients’ success, and each therapy participant’s OE can influence and/or interact with the other’s to create an important dyadic experience. Such therapist and dyadic OE can also bear on other key relational therapy processes and patient improvement. Encapsulating this interpersonal perspective in the context of CBT, the present chapter critically reviews three pertinent research threads: (1) studies that examined patient and/or therapist OE in relation to these therapy participants’ experiences of alliance quality; (2) a meta-analysis that examined the indirect effect of OE on treatment outcome through alliance quality; and (3) studies that tested dyadic OE patterns as predictors of therapy process and outcome—either in the form of one participant’s OE influencing the other’s or their OE attunement over time. We also discuss clinical implications of these threads and outline future research directions to advance OE science and practices.