Adolescence is an important period of increasing independence, when adolescents experience changing influences of family and friends on their diets as they transition into adulthood. We conducted a scoping review to map the literature on interpersonal determinants of diet quality and eating behaviors among individuals aged 13–30 years. We searched seven literature databases, and following screening, 329 papers were included. Determinants were grouped according to sub-categories of the Determinants of Nutrition and Eating framework: family structure (n = 122), social influences (n = 121), parental behaviors (n = 90), family food culture (n = 83), social support (n = 69), parental feeding styles (n = 24), parental attitudes/beliefs (n = 8), and parental resources/risk factors (n = 6), and we added two new sub-categories: parenting style (n = 74) and partner behaviors (n = 6). Fruit/vegetable (n = 143) and sugar-sweetened beverage (n = 102) intake were the most commonly measured diet outcomes, and breakfast consumption (n = 41) and fast food/takeaway intake (n = 39) the most commonly examined eating behaviors. This review highlights the gaps in the literature, both across the determinant sub-categories and also the relative paucity of longitudinal evidence and lack of evidence in emerging adults, particularly outside of university settings. Future research should focus on these areas to provide stronger evidence to support better design of interventions for this age group.