Research from other STEM disciplines suggests that a systems thinking approach can motivate students to learn content meaningfully and in a way that empowers them to use their knowledge to benefit the world around them. However, systems thinking is not currently widespread in chemistry education. As instructors' beliefs influence their classroom practices, professional development supporting the implementation of a systems thinking approach must explicitly address instructors 'perceptions of that approach. In the current study, we interviewed17 tertiary chemistry instructors who have experience using systems thinking in various chemistry courses in North America and Europe. According to the Interconnected Model of Teacher Professional Growth, the instructors' enactment of a systems thinking approach and their subsequent reflections on its outcomes allow them to provide unique insights into the affordances and constraints of a systems thinking approach. Study participants provided rich descriptions of how a systems thinking approach can benefit and challenge both students' learning and instructors' teaching in tertiary chemistry classrooms. Future professional development efforts could use each of these benefits and challenges to motivate potential adopters to implement a systems thinking approach and prepare them to address the challenges they or their students might encounter in using the approach.