Ensuring trainees develop the flexibility with their knowledge to address novel problems, and to efficiently build upon prior knowledge to learn new knowledge is a common goal in health profession education. How trainees come to develop this capacity to transfer and transform knowledge across contexts can be described by adaptive expertise, which focuses on the ability of some experts to innovate upon their existing knowledge to develop novel solutions to novel problems. While adaptive expertise is often presented as an alternative framework to more traditional cognitivist and constructivist expertise models, it is unclear whether the "non-routine" and "routine" forms of transfer it describes are distinct from those described by other accounts of transfer. Furthermore, whether "what" (e.g., knowledge) is transferred and "how" (e.g., cognitive processes) differs between these views is still debated. In this review, we describe various theories of transfer and present a synthesis clarifying the relationship between transfer and adaptive expertise. Informed by our analysis, we argue that the mechanisms of transfer in adaptive expertise share important commonalities with traditional accounts of transfer, which when understood, can complement efforts by educators and researchers to foster and study adaptive expertise. We present three instructional principles that may better support transfer and adaptive expertise in trainees: (i) identifying and incorporating meaningful variability in practice, (ii) integrating conceptual knowledge during practice (iii) using assessments of trainees' transfer. Taken together, we offer an integrative perspective to how educational systems and experiences can be designed to develop and encourage adaptive expertise and transfer.