Immune Mechanisms Breast cancer is the most common cancer in women. After completion of successful therapy, many behavioral symptoms persist with over 20% of breast cancer survivors reporting chronic insomnia of greater than 6 months duration that fulfils clinical diagnostic criteria with associated functional limitations, decreased quality of life, and possible effects on long-term survival. Behavioral interventions are highly efficacious in the treatment of insomnia and preferred over hypnotic medications when insomnia is chronic. However, insomnia studies conducted in cancer are scarce. The proposed research builds upon a program of study that has examined the efficacy of a mind-body intervention, Tai Chi Chih (TCC), on health outcomes including sleep impairments. Preliminary studies show that TCC, a slow moving meditation, contributes to improvements in subjective sleep quality, sleep amounts and sleep efficiency. We have further found that sleep, fatigue, and proinflammatory cytokine activity are reciprocally related and that TCC decreases proinflammatory cytokine levels. Thus, we further hypothesize that cytokine network is one physiological mechanism through which TCC carries its effects on sleep outcomes. In this randomized, controlled trial, 100 breast cancer survivors will be randomly assigned to TCC or sleep hygiene/education control (EC) over 16 weeks and followed for one year. The aims of this project are to: 1) evaluate the effects of TCC vs. EC on objective and subjective measures of sleep continuity, fatigue, and health functioning in breast cancer survivors with chronic insomnia;2) determine the effects of TCC vs. EC on measures of proinflammatory cytokine activity;3) evaluate whether circulating levels of proinflammatory cytokines temporally correlate with measures of sleep continuity in breast cancer survivors with insomnia over the course of the treatment trial. This project will constitute the first, randomized controlled clinical trial of the effects of TCC on sleep outcomes in breast cancer survivors, and will advance psychobiological models of insomnia treatment mechanisms.