Diet contributes to a large proportion of preventable deaths and diseases. Adolescence is a period during which diet may particularly evolve, and therefore represents an opportunity to develop long-lasting healthy dietary behaviours. However, dietary habits are particularly subject to social variations, which may lead to social inequalities in health. Tackling them requires public health actions based on a comprehensive approach of social determinants at this life stage. This doctoral thesis aimed to examine socioeconomic and sociocultural disparities in dietary habits among adolescents, using the repeated cross-sectional Health Behaviour in School-aged Children (HBSC) surveys conducted in French- and Dutch-speaking Belgian schools. The three specific objectives of this aim were: (i) to study the socioeconomic disparities in dietary habits of adolescents from different migration status; (ii) to determine trends in dietary disparities between 1990 and 2014; (iii) to estimate disparities in dietary habits according to the socioeconomic and migration status at both individual and contextual levels. Firstly, different socioeconomic disparity patterns according to the migration status were observed, with narrower disparities in 1st-generation immigrants than among natives, highlighting the major role of cultural influences in immigrant populations. Secondly, the long-term trend analyses emphasised increasing disparities for healthy foods and decreasing disparities for unhealthy foods. In addition, when the consumption of a food group increased overall, disparities decreased, and vice-versa. Finally, the multilevel analyses showed that individual and school disparities were independently associated with food consumption frequencies. Furthermore, this observational assessment revealed the weak relationships between nutrition policy in schools and dietary habits. Note that in the Brussels-Capital Region, native adolescents were at higher risk of unhealthy dietary behaviours than immigrants, but the risk of unhealthy ...