You will be paid up to $2760 for completing the entire study. Healthy men and women who smoke cigarettes and are 18 years old or older are needed to participate in a research study at the Johns Hopkins Bayview Medical Center. This is not a treatment study. The study tests factors that influence smoking behavior. Participation involves an initial phone screening and an in person 3 hour screening visit. If qualified, this study requires an additional 32 in person visits lasting approximately 4 hours each, and 4 in person visits lasting approximately 1.5 hours each. Afternoon and evening times are available for in-person visits. Principal Investigator: Matthew Johnson, Ph.D. Protocol #: IRB00107178