Adolescence is a critical period characterized by physical, social, and developmental changes that impact on health and eating behaviour. Indonesia is experiencing dramatic economic and infrastructural changes, causing greater access to the global food industry and media. This transition is influencing food intake trends, leading to new nutritional challenges in adolescent girls. Qualitative research was conducted between November 2016 and January 2017 in five urban sites in Java, Indonesia, to examine individual, social, environmental, and macrosystem factors affecting snacking behaviours in unmarried adolescent girls 16–19 years of age. Methods entailed 30 freelisting exercises, nine key informant interviews, and 16 in‐depth interviews. Freelisting results identified over 200 snack foods, with the most salient processed convenience foods such as chips and cookies. Respondents typically snacked multiple times daily. Widespread availability of affordable and “tasty” snacks makes snack foods appealing meal substitutes. Snacks provide a distraction to boredom and loneliness and an enhancement to social gatherings. Girls exhibited limited understanding or concern about potential negative effects of snacking. Parents facilitate acquisition of nutrient‐poor snacks, whereas friends exert pressure for routine consumption of snack foods. Social media infiltrated with promotions of eateries and snack foods is likely contributing to the preponderance of snack food consumption. Routine consumption of snack foods high in sugar, salt, and fat and skipping meals will likely have long‐term consequences on the nutritional status and health of Indonesian adolescent girls. Findings underline the urgent need to develop contextually relevant, targeted behavioural change strategies to modify the potentially harmful eating and activity patterns of adolescent girls identified in this study and to curb the trajectory of overweight in urban Indonesia.