Reducing population smoking prevalence is an urgent public health priority that can save more lives and money than almost any other known preventive intervention. Practical counseling, social support, and nicotine replacement therapy (NRT) are components of tobacco dependence treatment that increase the chances of cessation. Web-based interventions are a promising delivery channel for tobacco dependence treatment that have the potential for enormous public health impact (reach x efficacy). Millions of smokers use the Internet for cessation assistance each year and studies have shown quit rates of 7 to 26 percent. However, most users engage only minimally with even the best designed cessation websites, diminishing their impact due to limited exposure/use of effective treatment components (an insufficient dose). Poor adherence is documented across a range of Internet behavior change programs. Two approaches to improve adherence to Internet cessation treatment are integrating smokers into an online social network and providing free NRT. Active participation in online communities is associated with significantly higher rates of cessation. Proactive outreach to integrate smokers into a social network can increase perceptions of support and may also increase adherence to online problem solving/skills training tools and pharmacotherapy. Removing initial cost and access barriers to NRT can introduce smokers to medication who might not otherwise try it and may increase adherent use and outcomes. Provision of NRT may also increase adherence to practical counseling tools in Web-based cessation programs as smokers look for information on its use or side effects, and adherence to Web- based social support as smokers turn to others for support while quitting. The interaction of both strategies may exert the most powerful effects on adherence to all three components of cessation treatment. This study will compare the efficacy of an interactive, evidence-based smoking cessation website (WEB) alone and in conjunction with free NRT and a theory-driven, empirically-informed social network (SN) protocol designed to integrate participants into the online community. Using a 2 (access to free NRT, no access) x 2 (SN integration, no SN) randomized, controlled factorial design with repeated measures at baseline, 3, 9, and 15 months, this study will recruit N=4,000 new members of a Web-based smoking cessation program and randomize them to: 1) WEB, 2) WEB+SN, 3) WEB+NRT, or 4) WEB+SN+NRT. Hypotheses are that all three intervention conditions will outperform WEB alone and that WEB+SN+NRT will outperform WEB+NRT and WEB+SN on 30-day point prevalence abstinence measured at the primary endpoint of 9 months and at secondary endpoints of 3 and 15 months. Secondary aims and exploratory analyses will examine theory-driven hypotheses about the mediators and moderators of treatment outcome (e.g., social norms, social support, gender, motivation). Addressing adherence to Internet cessation programs is critical and timely to leverage the potential public health impact of this broad reach treatment modality. The proposed study is unconventional and innovative in its use of a social network intervention approach to improve both behavioral and pharmacological treatment adherence to enhance cessation outcomes. Understanding theory and basic mechanisms of behavior change is significant not only for reducing tobacco's devastating disease burden, but also for optimizing behavior change in other arenas where treatment adherence is just as critical.