Recent changes in special education in Switzerland have committed several provinces to promote the inclusion of children with special educational needs (SEN) in general education classrooms. As teachers’ attitudes toward inclusive policies are a key element of their successful implementation, the present study investigates factors related to teachers’ attitudes toward inclusive education, using an explanatory sequential design. In the quantitative phase, questionnaires were sent out to 600 elementary school teachers from three Swiss provinces. A total of 336 regular teachers completed both the Opinion Relative to the Integration of students with disabilities scale and the Attitudes Toward Inclusive Education Scale. Quantitative results indicate that several factors had an impact on teachers’ attitudes toward inclusion: type of disability, teacher’s self-efficacy beliefs about teaching students with SEN, previous experience in teaching students with SEN, years of teaching experience, and knowing someone with a disability. Teachers’ attitudes did not appear to vary according to gender or inservice training in disability and inclusive education. In the subsequent qualitative phase, eight in-depth interviews were conducted in order to explain quantitative results. Findings highlight the important factors to be taken into account in preparing and supporting teachers with the inclusion of students with special educational needs.