This review systematically synthesizes empirical evidence on learning outcomes of interdisciplinary learning. A meta-synthesis approach was used to synthesize data in two rounds, based on strict (n = 38) versus more lenient (n = 60) operationalizations of interdisciplinary learning. The results revealed a variety of interdisciplinary learning outcomes that were categorized into three overarching themes: 1) academic and disciplinary engagement, 2) metacognitive skills, and 3) perspective taking skills. Process results revealed that empirical evidence in the field is still in its infancy. The findings of this review can be considered as a starting point for the further operationalization of interdisciplinary learning outcomes, so that robust evidence for various aspects of interdisciplinary learning can be collected, and compared with other forms of learning such as cross or transdisciplinary learning.