This thesis aims to investigate the initial motivation and motivational development of mathematics and science students and student teachers in response to the impending shortage of subject teachers in Finland. For this purpose, students’ motivation for teaching and student teachers’ motivational development were assessed in a two-part mixed-method study. First, an online survey was conducted among 50 first-year mathematics and science students to explore their intention to become teachers as well as their motivations for and perceptions of teaching. The results show that students consider intrinsic value, prior teaching and learning experiences, and perceived teaching abilities as most relevant for the career choice of teaching. The teaching profession is perceived as high in demand and lower in return. Differences in motivation and perceptions were partly found in relation to the intention to pursue teacher education. Second, in semi-structured interviews with seven student teachers, motivational development was found to shift especially during the pedagogical studies, with supportive supervising teachers, fellow students, and perceived professional competence being positively related to motivation for teaching. The findings suggest that both initial motivation and motivational development are crucial for entry into the teaching profession. Future research should address the limitations of small convenience samples and the unsatisfactory psychometric quality of survey instruments by conducting longitudinal studies with larger samples from different Finnish universities.