In Europe, the diversity of medical coding systems used in electronic health data creates significant challenges in defining and retrieving study variables consistently across datasets. A concept defined in one coding system cannot be directly applied in another without harmonisation. The VAC4EU Code List tackles this issue by offering a centralised, semi-automated platform built on the CodeMapper system for creating harmonised, multilingual, and version-controlled codelists. These codelists serve as reusable, metadata-rich reference standards that can be tailored and reused in future studies, promoting consistency and transparency across projects.