OpenRefine (formerly Google Refine) is a powerful, open-source desktop application for working with messy data, offering capabilities for cleaning, transforming, and extending datasets. Originally developed by Metaweb and later supported by Google before becoming an independent open-source project, OpenRefine operates through a browser-based interface while running locally on your computer, ensuring your data never leaves your machine. The tool excels at clustering algorithms for finding and merging near-duplicate entries, supports reconciliation against external services like Wikidata and VIAF, and provides a complete undo/redo history that makes all transformations reversible and reproducible. A key strength is OpenRefine's faceting and filtering system, which allows you to slice data along multiple dimensions simultaneously, and its GREL (General Refine Expression Language) for complex data transformations. Understanding that OpenRefine works in rows mode (where each row is independent) versus records mode (where multiple rows can be linked together) is fundamental to mastering multi-valued cell operations and maintaining relational structure during transformations.