The evolution of urban planning education in the United States has undergone four eras: First, from the early to mid-twentieth century, professionals from select disciplines and fields collaborated and institutionalized planning education. Second, during the mid-twentieth century, there were tensions between design/physical planning and policy/social sciences, as well as generalist and specialist education. Third, from the mid- to the late-twentieth century, there was institutionalization through recognition and accreditation. Fourth, since the late-twentieth century, planning education has transitioned to studio instruction and internationalization. In an evolving fifth era, triggered by sustainability, planning education is transitioning from interdisciplinarity to transdisciplinarity.