Choosing a field of study is an important decision in determining future educational trajectories and occupations, and we know that boys and girls make different field of study choices. Girls are underrepresented in gender-stereotypical masculine fields like science and technology, whereas boys are underrepresented in gender-stereotypical feminine fields like education or health-related fields. This dissertation provides insight in the different ways in which adolescents’ social environment affects field of study choices, with a specific focus on how it leads boys and girls to different fields. It examines the role of internalized gender ideologies as well as the influence of parents, siblings, and friends. It does so by contrasting two theories.Gender-role socialization theory states that boys and girls choose different fields of study because they learn from their social environment what is “appropriate” male or female gender-role behavior. Resource theory states that adolescents’ social environment transfers field-specific resources (e.g., information, skills, aspirations) that adolescents can draw upon to make a field of study choice. This dissertation concludes that both theories have their merit depending on which aspect of the social environment we focus on. On the one hand - in line with gender-role socialization theory - internalized gender ideologies, mothers’ and friends’ increase gender differences in fields of study. First, internalized ideas of what is “appropriate” male or female gender-role behavior (gender ideology) contributes to gender inequality in educational fields because it leads boys to more masculine fields of study in secondary education. Second, mother’s occupation functions as an example of “appropriate” female gender-role behavior, which guides girls to more feminine and boys to more masculine fields of study. This highlights the need to include mothers – next to fathers – in studying adolescents’ field of study choices. Lastly, friends who have more traditional gender ideologies ...