Objectives: This systematic review aimed to examine hip rotator range of motion (ROM) and strength values across athletic, injured, and non-active populations, and to determine how these values differ when measured at different hip flexion angles. Methods: A systematic literature search was conducted in accordance with PRISMA guidelines across six electronic databases (PubMed, Scopus, Web of Science, SPORTDiscus, CINAHL, and Medline) from inception to June 2025. Eligible studies included observational, cross-sectional, case-control, or randomized controlled trial (RCT) studies that quantitatively assessed hip IR/ER ROM and/or strength in defined population groups (athletic, injured, or non-active). Two reviewers independently screened titles, abstracts, and full texts, extracted data on study design, population characteristics, measurement methods, and outcome variables, and assessed risk of bias using an established tool. Discrepancies were resolved by a third reviewer. Results: 11 studies met the inclusion criteria, including 1276 participants across athletic, injured, and non-active populations. Hip rotator ROM was measured in nine studies and strength in three, with varying testing angles (0° and/or 90° hip flexion). Overall, athletes showed greater ROM at 0° compared to injured and non-active groups, but had reduced ROM at 90° relative to non-active participants. Non-active individuals had the lowest ROM at 0°. Strength findings, though limited, indicated higher values at 90° than at 0°. Conclusions: Hip rotator ROM and strength vary across populations and testing angles, with ROM generally lower and strength higher at 90° of hip flexion. Due to methodological inconsistencies, findings should be interpreted as directional evidence, reinforcing the need for standardized assessment protocols in future research.