The proposed development study entitled, Tailored Mobile Text Messaging to Reduce Problem Drinking is designed to develop and test a tailored adaptive text messaging/short message service (SMS) intervention for individuals interested in stopping or reducing their alcohol consumption. This intervention includes messages tailored to baseline assessment results (including drinking times) that are adaptive to ongoing drinking patterns and goal achievement via interactive ecological momentary assessment (EMA). Other features include participant initiated help messaging and support network alerts. We will conduct beta research with 40 problem drinkers to assess messaging preferences and acceptability, and then conduct a pilot test with 10 PDs. In Stage 1b, we aim to test this intervention and understand the mechanisms of action of different text messaging interventions with 200 problem drinkers over a 12-week period. We propose to compare four types of messaging: 1) Tailored content and timed messaging adaptive to the participants current state (Stage 1a intervention); 2) Tailored content messaging (not adaptive or timed) sent at 3 pm every day; 3) Untailored consequence based messages sent at 3 pm every day; and 4) Brief feedback and EMA only. Assessments will be completed at baseline, through weekly EMA via SMS and at week 12 via a web-based follow-up assessment. Primary outcomes include drinks per drinking day, days of heavy drinking, and average drinks per week as measured through weekly EMA. Additional outcomes will include drinking related consequences, goal commitment and intervention satisfaction. Outcomes will be used to modify the intervention and to prepare for a larger Stage 1c RCT.