Aim/Purpose: This systematic literature review investigates the underlying factors that influence the gap between the popularity of online learning and its completion rate. The review scope within this paper includes an observation of possible causal aspects within the non-ideal completion rates in online learning environments and an identification of recommended strategies to increase retention rates. Background: While online learning is increasingly popular, and the number of online students is steadily growing, student retention rates are significantly lower than those in the traditional environment. Despite the multitude of studies, many institutions are still searching for solutions for this matter. Methodology: A systematic literature review was conducted on 40 studies published between 2010 and 2018. We established a set of criteria to guide the selection of eligible articles including topic relevance (aligned with the research questions), empirical studies, and publication time frame. Further steps were performed through a major database searching, abstract screening, full-text analysis, and synthesis process. Contribution: This study adds to expanding literature regarding student retention and strategies in online learning environments within the higher education setting. Findings: Revealed factors include institutional support, the level difficulty of the programs, promotion of a sense of belonging, facilitation of learning, course design, student behavioral characteristics, and demographic variables along with other personal variables. The recommended strategies identified for improving student retention are early interventions, at-all-times supports for students, effective communication, support for faculty teaching online classes, high-quality instructional feedback and strategies, guidance to foster positive behavioral characteristics, and collaboration among stakeholders to support online students. Recommendations for Practitioners: Since factors within the open systems of online learning are interrelated, we recommend a collective effort from multiple stakeholders when addressing retention issues in online learning. Recommendations for Researchers: We recommend that fellow scholars consider focusing on each influential factor and recommendation in regard to student retention in online learning environments as synthesized in this study. Findings will further enrich the literature on student retention in online learning environments. Future Research: Future research may investigate various data-mining and analytics techniques pertaining to detection and prediction of at-risk students, the efficacy of student support and faculty support programs, and ways to encourage struggling students to adopt effective strategies that potentially engender positive learning behaviors.