The purpose of this study is to test the effectiveness of a behavioral weight loss and exercise intervention delivered via the internet at different cancer centers in New England. The investigators hypothesize that participants will lose 7% of their body weight. The research is being done because many women who are treated for breast cancer are overweight and treatment for breast cancer is often accompanied by weight gain. Individuals who are overweight may be more likely to have their breast cancer come back. Also women who exercise at least three hours a week seem to have less chance of their cancer coming back. The investigators hope to identify an effective weight loss and exercise intervention for breast cancer survivors that can be easily accessed by many people.

This study is designed to determine the feasibility of conducting a distantly delivered-weight loss and exercise intervention for patients who have been treated for breast cancer at three cancer centers, and to evaluate the efficacy of an Internet-based behavioral weight loss and exercise intervention delivered to overweight/obese breast cancer survivors in three New England locations.

Participants will be recruited from three New England Cancer Centers - the Vermont Cancer Center, Norris Cotton Cancer Center at Dartmouth University and the University of Massachusetts Cancer Center. Participants from each center will undergo baseline assessments that include diet assessment, body measurements (height, weight, etc), a physical activity assessment and be asked to complete a series of questionnaires.

Patients that meet the minimum requirements will be enrolled on the study. They will participate in weekly on-line "chats" about behavioral and diet modifications led by a qualified facilitator. Participants will also engage in increasing amounts of aerobic activity (typically walking) throughout the course of the intervention. The intervention lasts 6 months. At the end of those 6 months, participants will have the same assessments that were collected at baseline. Following the collection of those assessments, participants will have completed the study.

Inclusion Criteria:

• breast cancer diagnosis
• Completion of surgery, chemotherapy +/- radiation for stage I, II, or III breast cancer 2-12 months prior to study initiation
• BMI between 27 and 50
• patient self-report of ability to walk for 10 minutes without interruption or pain
• access to computer and the internet

Exclusion Criteria:

• metastatic disease
• prior receipt of chemotherapy for other malignancy
• pregnancy at the time of study entry
• limited food choices due to celiac sprue or inflammatory bowel disease
• illiteracy
• non-English speaking