The benefits of a compulsory internship in environmental science education were investigated with respect to the three institutional goals of university education: (1) training for research; (2) professional education; and (3) general natural science education. A survey examined which student qualifications are improved by an internship complementary to traditional university education. The survey assessed 14 qualifications of students participating in a compulsory 15-week internship in the 5-year diploma program at the Swiss Federal Institute of Technology (ETH Zurich). Pre- and postinternship questionnaires of 478 students and 293 supervisors are included. Results indicated that internships enhance general abilities and key qualifications, such as communication skills, report writing, organization of work, information acquisition, and the ability to operate independently. This suggests that internships are of high value to professional education. However, internships also seem to promote salient qualifications of complex environmental problem solving which are relevant for the development of research capabilities in environmental sciences.