) Insomnia and fatigue commonly occur during and/or after cancer treatment. While variable by diagnosis and stage of illness, 30-60% of cancer patients endorse difficulty initiating and/or maintaining sleep and 50-90% endorse fatigue. Despite these high prevalence rates, and the substantial overlap in occurrence, most research related to cancer-related fatigue (CRF) has assessed this pervasive and persistent symptom in a manner that does not take into account sleep quality and quantity. This is, in part, due to the definition of CRF as “pathological levels of persistent physical, emotional, and/or cognitive ‘enervation’ that appear not to be relieved, or improved by, rest or sleep”. To date only a few studies have evaluated whether behavioral treatments such as Cognitive Behavioral Therapy for Insomnia (CBT-I) can provide some relief to patients who are experiencing CRF. The effect sizes for CBT-I outcomes, in the context of cancer, have been found to be comparable to those observed in “primary insomnia”. The findings with respect to CBT-I effects on CRF have been more modest. The smaller effects of CBT-I on CRF may be due to a variety of factors, but one simple possibility is that CBT-I is under-dosed for patients with cancer. In other words, subjects with cancer may require more sessions to achieve sleep durations that can affect daytime fatigue. Accordingly, we propose to evaluate the association between CBT-I dose (Low dose [4 or 8 sessions] or High Dose [10 or 12 sessions]) and changes in sleep duration and CRF. The study will enroll 70 subjects to obtain an analysis sample of 60 subjects. Subjects will be diagnosed with breast cancer and will be between the ages of 25-85 (inclusive). In order to allow age to be an analyzable factor, recruitment will be stratified so that the following cohorts are equally populated (i.e., 25-45, 45-65, 65-85). The focus of the R21 study will be on feasibility. The primary outcomes will be related to recruitment, subject adherence, treatment acceptability, and subject retention. Descriptive data will also be obtained to examine whether high dose CBT-I (i.e., larger improvements in sleep efficiency and/or sleep duration) positively affects CRF. The study will be undertaken in collaboration with our program post doc (Dr. Muench) as she transitions to Jr. Faculty and pursues this program of research on a more independent basis. The study collaborators will also include: Dr. Knashawn Morales (statistics); Dr. Sheila Garland (psycho-oncology & sleep); and Dr. Donn Posner (CBT-I).