This chapter discusses different factors underpinning the development of online doctoral education and pedagogical concerns influencing the design of online doctoral programs. The rapid development of online doctoral education has been guided by recent changes in doctoral education and distance education contexts, both conceptually and empirically. To develop a comprehensive understanding of the nature of online doctoral education, 47 journal articles concerning the design of existing online doctoral programs were systematically selected and reviewed. The review results demonstrate that online doctoral education is a complex entity developed and influenced by a dynamic interplay among multiple factors relevant to different aspects of online higher education, professional doctoral education and internationalized education. However, there has been a lack of holistic research approaches to develop a comprehensive understanding of online doctoral education. In particular, literature grounded in online higher education and professional doctoral education scholarship has not been effectively integrated and synthesized, creating an unhelpful chasm. Within the chasm, a range of pedagogical concerns and contradictions have emerged in online doctoral programs, which can be understood and addressed only when online doctoral educators have a holistic perspective bridging the two. Therefore, while the present review reveals valuable insights into online doctoral education research and practice, it also suggests that more research needs to be conducted using a more comprehensive theoretical understanding of online doctoral students and their experiences.