Objective To develop and validate the Weight Control Strategies Scale (WCSS), a self-report instrument to assess use of specific behaviors thought to facilitate weight loss. Design and Methods Factor analysis was conducted on 323 overweight and obese adults (mean age=48.7±10.9 years, mean BMI=35.4±4.9 kg/m2, 74% female) enrolled in three different behavioral weight loss trials who completed the WCSS prior to starting treatment. To evaluate construct validity, additional data on dietary intake, physical activity, treatment session attendance, and weight change were obtained from a subsample of participants before and after participation in a 48-week weight loss program. Results Principal components analysis with varimax rotation revealed a four component solution for the WCSS, representing the following subscales: Dietary Choices, Self-monitoring Strategies, Physical Activity, and Psychological Coping (a’s from 0.79–0.89). Longitudinal analyses showed that WCSS subscale scores increased during treatment (p’s <0.01). In adjusted models, changes in WCSS total and subscale scores were associated with posttreatment weight loss (p’s <0.01). Additionally, changes in WCSS Dietary Choices and Physical Activity subscales were related to posttreatment changes in total daily kilocalorie consumption (p=0.019) and weekly kilocalorie expenditure through physical activity (p<0.001), respectively. Conclusions Findings support the validity and reliability of the WCSS in a weight loss treatment seeking sample.