Abstract: Loneliness is receiving more and more attention for being an important psychosocial contributor to the deterioration of quality of life, psychological well-being, onset of mental health disorders, but also to the increased mortality and morbidity, through the mediation of general health problems and suicide. While studies on the impact of loneliness in the civilian population have been steadily increasing in number over the past decade, research on the same phenomenon in military settings has progressed at a comparatively slower pace. This article is a two-stage analysis of the perceived lack of social connectedness among active-duty and former military personnel, including (1) a conceptual exploration and literature review based on searches in three electronic databases (PubMed, Google Scholar, and Web of Science/Clarivate), and (2) a pragmatical set of recommended strategies to reduce the impact of loneliness in these populations. Based on the review of 42 primary and secondary sources, the paper explores the prevalence, risk and protective factors, characteristics, and consequences of loneliness, with particular attention to various minorities, female military personnel experiencing motherhood during active duty, civilian spouses of deployed service members, and other significant subgroups. Recommended directions of interventions are threefold, i.e., screening for loneliness and its risk factors, initiation of prophylactic strategies and therapeutic interventions targeting this phenomenon in vulnerable categories. In conclusion, further research on loneliness in both active and former military personnel is strongly warranted, given its significant consequences for multiple dimensions of health and overall functioning.