One goal of education is to help students become well-rounded citizens who can think broadly across boundaries. In addition, individuals with interdisciplinary thinking skills can be valuable contributors to modern research challenges by understanding and recognizing interdisciplinary connections and working in diverse teams. However, little research exists on the connection between interdisciplinary thinking and physics education. What aspects of physics classroom practices and experiences foster interdisciplinary thinking? What effect does interdisciplinary thinking have on the development of students' physics identities? Using a physics identity theoretical framework with data from a national survey, this study found that self-reported characteristics of interdisciplinary thinking are significantly correlated with higher levels of physics identity development. Also, several factors of the physics classroom environment and pedagogies are significantly related to interdisciplinary thinking.