In Taiwan, several nationwide registries provide high-quality data for causal inference and pharmacoepidemiology research, including the Rare Disease Database, COVID-19 Vaccine and Record Database, Assisted Reproduction Database , Registry for Catastrophic Illness Patients, Taiwan Cancer Registry, Birth Certificate Application database, Death Registry, and the Traditional Chinese Medicine database. Each registry captures disease- or treatment-specific information with standardized variables and, importantly, can be linked to the National Health Insurance Research Database through encrypted identifiers. Such linkage allows researchers to identify patients’ longitudinal diagnoses, prescriptions, and healthcare utilization. These interconnected databases enable comprehensive real-world analyses of disease progression, treatment patterns, safety and effectiveness.