Background The practice pattern and outcome of medical devices following their regulatory approval may differ by country. The aim of this study is to compare postapproval national clinical registry data on transcatheter aortic valve replacement between the United States and Japan on patient characteristics, periprocedural outcomes, and the variability of outcomes as a part of a partnership program (Harmonization-by-Doing) between the 2 countries. Methods and Results The patient-level data were extracted from the US Society of Thoracic Surgeons /American College of Cardiology Transcatheter Valve Therapy (STS/ACC TVT) and the J-TVT (Japanese Transcatheter Valvular Therapy) registry, respectively, to analyze transcatheter aortic valve replacement outcomes between 2013 and 2019. Data entry for these registries was mandated by the federal regulators, and the majority of variable definitions were harmonized to allow direct data comparison. A total of 244 722 transcatheter aortic valve replacements from 646 institutions in the United States and 26 673 transcatheter aortic valve replacements from 171 institutions in Japan were analyzed. Median volume per site was 65 (interquartile range, 45-97) in the United States and 28 (interquartile range, 19-41) in Japan. Overall, patients in J-TVT were older (United States: mean-age, 80.1±8.7 versus Japan: 84.4±5.2; <0.001), were more frequently women (45.9% versus 68.1%; <0.001), and had higher median Society of Thoracic Surgeons Predicted Risk of Mortality (5.27% versus 6.20%; <0.001) than patients in the United States. Japan had lower unadjusted 30-day mortality (1.3% versus 3.2%; <0.001) and composite outcomes of death, stroke, and bleeding (17.5 versus 22.5%; <0.001) but had higher conversion to open surgery (0.94% versus 0.56%; <0.001). Conclusions This collaborative analysis between the United States and Japan demonstrated the feasibility of international comparison using the national registries coded under mutual variable definitions. Both countries obtained excellent outcomes, although the Japanese had lower 30-day mortality and major morbidity. Harmonization-by-Doing is one of the key steps needed to build global-level learning to improve patient outcomes.