As a prerequisite for all adult learners in life-long learning, self-directed learning has been constantly discussed since the early 1960s. However, in what manner research operationalizes the concepts and what similarities occur across the empirical studies and theoretical studies are still ambiguous. The purpose of this study is to employ an integrative literature review to investigate and disentangle various interpretations of self-directed learning by identifying how the topic is defined and what competencies and strategies are needed for a highly self-directed learner. This is a six-phase study, including: 1) problem formulation; 2) data collection; 3) problem re-formulation; 4) data evaluation; 5) data collection; and 6) presentation of the findings. This study provided a comprehensive perspective of self-directed learning in a dynamically expanding process to include multifaceted interpretations of the topic and advanced research in self-directed learning in an updated, enriched learning environment. Specifically, the researcher updated the evidence for self-directed learning to date, identified all of the potential dimensions of self-directed learning that distinguish a highly-directed self-directed learner and the related instructional strategies, and made suggestions for the future direction of research on the topic.