Given the growing contribution of snacks to dietary intake and the need for effective strategies to reduce obesity, it is important to consider whether snacking behaviors contribute to high BMI in childhood. This review summarizes US research that has addressed trends in snacking behavior and its contribution to dietary intake, as well as research describing snack food availability in settings where youth spend their time. In addition, it comprehensively reviews studies conducted in the United States and internationally that have examined associations of snacking behavior with weight. Research published between January, 2000, and December, 2011, was identified by searching PubMed and MEDLINE databases, and by examining bibliographies of relevant studies. Recent analyses of trends in dietary intake have shown there were significant increases in the contribution of energy-dense, nutrient-poor foods to snacking kilocalories over the past few decades. Although snacks can contribute to intake of key nutrients, frequent snacking has been associated with higher intake of total energy and energy from added and total sugars. Assessments in schools and retail stores have further indicated that energy-dense, nutrient-poor snacks are widely available in settings where youth spend their time. The majority of studies either found no evidence of a relationship between snacking behavior and weight status or found evidence indicating that young people who consumed more snacks were less likely to be obese; however, additional research is needed to address various methodological limitations. Recommendations for future research are provided to address knowledge gaps and inform the development of interventions.