Based on an expectancy-value theoretical framework and data (n = 1654) collected in 29 Finnish municipalities using a structured questionnaire, this study examines primary (grades 5-6), lower secondary (grades 7-9) and upper secondary (grades 10-12) students' motivation in music and mathematics. It explores in detail the students' interest in music and mathematics inside and outside school, primarily from the point of view of enjoyment of the subject and the perceptions about the importance and usefulness of the subject. However, it also investigates the respondents' view of the difficulty of the subject, the popularity of the subject, self-competence in the subject, and gender. The main results are: 1) In general, music is a more interesting subject than mathematics, but it is more interesting outside school than in school. Mathematics is more interesting in school and girls are more interested in music, whereas boys are more interested in mathematics, 2) Interest in music and mathematics inside and outside school can be explained by the enjoyment related to studying the subjects and the view of the importance and usefulness of the subjects, and 3) An intrinsic motivation in mathematics strengthens a positive relationship with music.