This article follows calls in the HRD literature to support multiteam system (MTS) learning. The objective of this article is to review the literature on external team learning (i.e., learning outside teams) to provide insight about team learning in MTSs and associated recommendations for future research. A review of 51 studies (42 quantitative, 10 qualitative) from 42 papers is guided by fundamental questions about how to enact external team learning (i.e., what, who, and when) and how to ensure a psychologically safe environment to foster that learning. The primary impact of this review is to the scholarly literature on external team learning and MTSs by identifying considerable overlap between these topics and nuances about each that have yet to be sufficiently assessed. The findings from this review provide the basis for nine recommendations for future research on theory, methods, and practical applications of external team learning.