The rising prevalence of obesity in the United States is believed to be due to increased exposure to adverse environmental factors, such as food portion sizes and increased dietary variety. Although decreasing portion sizes is a strategy used in weight loss programs, research has not studied the effects of decreasing dietary variety. Cross-sectional studies show a positive association between variety and body weight and in our own studies we have shown that greater reductions in the number of different snack foods (i.e. cookies, chips) consumed predicted greater decreases in overall caloric and fat intake and greater weight loss. Limiting variety may reduce intake through long-term sensory-specific satiety and/or monotony. Reducing dietary variety is a novel dietary approach with the potential to improve long-term weight loss, which has not been studied as a clinical strategy in obesity research. The objective of this application is to conduct a randomized controlled trial of a behavioral weight loss intervention limiting the number of different snack foods consumed. Two hundred overweight and obese participants will be randomized to a standard behavioral intervention (Standard) or to a standard behavioral intervention that also limits the number of different snack foods consumed (Limited Variety). Both conditions will receive an 18-month standard behavioral intervention, using behavioral techniques (i.e., self-monitoring) to change eating behaviors. Participants in the Limited Variety condition will also limit variety in snack foods to only two chosen snack foods throughout the intervention. Measures of weight, snack food consumption and hedonics, and diet satisfaction will be taken at 0, 6, 12, and 18 months. This investigation will determine: 1) if the Limited Variety condition produces greater weight loss than the Standard condition at 18 months; 2) if the Limited Variety condition consumes fewer servings and calories from snack foods than the Standard condition; and 3) if limiting snack food variety produces long-term sensory-specific satiety and/or monotony. Relevance: Experimental studies show that limiting dietary variety profoundly reduces intake. To date, there is no dietary prescription that has been tested that capitalizes on the effect of variety on intake that can be maintained. This will be the first investigation to examine methods of manipulating dietary variety that can be adhered to over time and that influence intake, weight loss, and weight loss maintenance.