The general view among researchers is that a well-functioning democracy rests in the handsof the political behaviour of citizens. In this behaviour, political interest is one of thecornerstones. Thus, there are reasons to regard it as a threat to democracy when young peopletend to have ever-lower levels of political interest. Therefore, to know how interest couldincrease, there is a need to know where it comes from and why it differs. There is yetuncertainty regarding this, notably since political interest as a concept rarely is used as adependent variable. Consequently, this thesis was aimed to explain why political interestdiffers among upper-secondary school students in Sweden. The focus was on the two types ofnational programmes, political socialization and socio-economic background. The findings of survey data (N=398) suggest that the average youth has low levels of politicalinterest. As hypothesized, there are, on average, higher levels of political interest amongstudents in preparatory academic programmes compared to vocational programmes. Alonethough, this pattern cannot explain variations of interest. Instead, agents of politicalsocialization have strong explanatory power, in particular friends and media. Also, family dohave a direct effect on political interest. However, this relationship appears to be dependent onsocio-economic background. The school as a political socialization agent cannot explaindifferences in political interest.