Treatment adherence is a challenge for Internet behavior change programs. The ubiquity of mobile devices and their effectiveness in promoting adherence in other areas of health behavior change make them a promising tool to address adherence in Internet interventions. Text messaging is accessible and easy to use; messages can proactively prompt/remind and encourage continued exploration of a web-based intervention; interactive text messaging can facilitate engagement with core Internet intervention components. Phase I of this two-phase study uses a factorial design to test the impact of 4 experimental text message features on adherence to a web-based intervention. Phase II will be a 2-arm randomized trial to compare the efficacy of a web-based cessation program alone and in combination with the text message intervention from Phase I on smoking outcomes.