Abstract: Military service in the post-9/11 generation is often mentally, emotionally, and physiologically stressful, putting service members at risk for mental health issues. Resilience protects against stress-related mental health issues and is valued by the United States military. However, resilience is often challenging to accurately evaluate and effectively promote. This study was intended to examine the relationship between resilience and posttraumatic stress disorder in post-9/11 active-duty United States service members and explore evidence that heart rate variability could be valuable data used in the determination of resilience or risk for posttraumatic stress disorder. This project utilized an evidence-synthesis methodology and a systematic literature review research design that followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to examine 26 published research articles that fit the strict eligibility criteria for this study. Based on the themes that emerged, it was concluded that significant clinical consideration should be given to the use of heart rate variability as an accurate and non-invasive way to measure and promote resilience and protect against posttraumatic stress disorder in service members. Due to the limited amount of literature that was available on this topic, it was concluded that future studies using a combination of psychological and biological research approaches, data, and strategies with a large and diverse active-duty military population will help to expand the results.