Background and Purpose: Action Observation Therapy (AOT) has been proposed to improve gait, balance and mobility in subjects with neurological and musculoskeletal disorders. The current review aimed to investigate AOT effects in subjects with gait, balance and mobility impairments., Methods: A systematic literature search was performed using PubMed/MEDLINE, EMBASE and Scopus databases from inception until May 2023. Randomized controlled trials investigating effects of AOT on gait, balance and mobility in subjects with any type of clinical condition were included. Two reviewers performed data extraction and methodological quality assessment using the revised Cochrane risk of bias tool for randomized trials. The overall effects were reported as mean difference (MD) or standardized mean difference (SMD) with 95% confidence interval (CI)., Results: Thirty-one studies were included. Low evidence supported AOT to enhance walking speed (SMD: 0.40; 95% CI: 0.17, 0.62; I 2 = 0%), stride length (SMD: 0.35; 95% CI 0.05, 0.66; I 2 = 0%) and single limb support duration (MD: 4.1%; 95% CI: 1.0, 7.2, I 2 = 0%) after stroke. Low evidence supported AOT to improve walking distance (MD: 56.8 m; 95% CI; 39.2, 74.4 m) and dynamic (SMD: 0.40; 95% CI: 0.04, 0.76; I 2 = 0%) and static (SMD: 0.69; 95% CI: 0.32, 1.05; I 2 = 0%) balance, while very low evidence supported AOT to enhance mobility (MD: -1.48 s; 95% CI; -2.2, -0.8 s; I 2 = 0%) after stroke. Moderate evidence supported AOT to improve dynamic balance in subjects with Parkinson's disease (SMD: 0.44; 95% CI: 0.09, 0.79; I 2 = 28%), while low evidence supported AOT to enhance dynamic balance (SMD: 0.61; 95% CI: 0.15, 1.08; I 2 = 27%) and mobility (MD: -2.08 s; 95% CI; -3.5, -0.6 s; I 2 = 0%) in patients with orthopedic conditions., Conclusion: AOT improved gait, balance and mobility after stroke, dynamic balance in patients with Parkinson's disease and dynamic balance and mobility in patients with orthopedic conditions. However, evidence certainty was generally low and further high-quality studies are needed., Trial Registration: PROSPERO International Prospective Register of Systematic Reviews (n. CRD42021240626)., (© 2024 John Wiley & Sons Ltd.)