Thirty nicotine-dependent cigarette smokers with Bipolar I Disorder will be enrolled (N=30). All subjects will be symptomatically stable prior to enrollment, and compliant with their mood-stabilizer medication treatment to minimize the chances of adverse outcomes. The treatment group would receive flexible doses of varenicline (VAR) ranging from one to four capsules (0.5-2.0 mg) orally per day. The control group would receive one to four capsules of placebo VAR (0 mg) orally per day. All subjects would receive weekly Cognitive Behavioral Therapy (CBT) offered in group format to help them deal with tobacco cravings and mood management. The target quit date would be set during Week 3 of the trial. Comprehensive neuropsychological assessment and laboratory testing will be given at baseline and ten weeks;