Despite the well-established evidence that many breast cancer survivors encounter some degree of difficulty regarding their sexuality, support for women and couples experiencing sexual difficulties as a result of breast cancer is lacking. The purpose of this dissertation was to develop and evaluate an online psychosexual intervention for couples experiencing sexual difficulties following breast cancer. The feasibility, acceptability, and preliminary impact of the intervention were evaluated using a single-arm, mixed-methods design, with participants completing questionnaires concerning sexual functioning, marital quality, and psychological adjustment at baseline, post-treatment, and three-month follow-up, along with satisfaction surveys and post-treatment interviews Participants subjective experiences were triangulated with the quantitative data as a form of cross-verification, and to capture a more nuanced understanding of couples experiences with this intervention and its delivery, along with its benefits. A sample of 14 couples (N = 28) received a 6-session psychosexual intervention delivered via videoconferencing (eTherapy). The intervention was found to be feasible and acceptable, as demonstrated by high retention, treatment adherence, and satisfaction. There was also evidence to suggest that the intervention was effective at improving sexual functioning and satisfaction, although decreasing effect sizes at 3-month follow-up point towards a progressive loss of gains on a number of measures over time. The use of eTherapy was widely accepted by participants, who highlighted several advantages of this modality. Overall, the results support the effectiveness of this eTherapy psychosexual intervention for couples affected by breast cancer. Emerging considerations for researchers and clinicians involved in the evaluation and implementation of psychosexual interventions, as well as in the provision of eTherapy, are also introduced