The *refractiveindex.info* database is a comprehensive, open-source repository of optical constants for a wide range of materials. The database aims to advance research in optics and photonics by providing accurate and reliable data. The data is sourced from peer-reviewed publications, manufacturer datasheets, and authoritative texts, ensuring its reliability and accuracy. Each entry in the database includes detailed metadata, facilitating comprehensive understanding and efficient utilization of the data. The data is stored in a YAML-based format, ensuring integrity, consistency, and ease of access. The YAML format allows for easy parsing and manipulation by both users and computer programs. The database includes both linear and nonlinear optical properties, with the nonlinear properties (n2) being a recent addition to address the challenges of high-power lasers. The collection process involves systematic data extraction from various sources, including scientific papers, manufacturer catalogs, and online databases. Data extraction is verified through manual comparison, plot comparison, and cross-entry comparison to ensure accuracy. The database is regularly updated to incorporate new data and improvements. Users can access the database through the RefractiveIndex.INFO website or via Python scripts that facilitate data retrieval and analysis. The database is also available on GitHub, where additional scripts and tools are hosted. The dataset is publicly available under a Creative Commons Zero license, allowing unrestricted use, distribution, and modification. The *refractiveindex.info* database is an essential tool for researchers, engineers, and students working in the field of optics and photonics, providing a comprehensive and reliable source of optical constants.The *refractiveindex.info* database is a comprehensive, open-source repository of optical constants for a wide range of materials. The database aims to advance research in optics and photonics by providing accurate and reliable data. The data is sourced from peer-reviewed publications, manufacturer datasheets, and authoritative texts, ensuring its reliability and accuracy. Each entry in the database includes detailed metadata, facilitating comprehensive understanding and efficient utilization of the data. The data is stored in a YAML-based format, ensuring integrity, consistency, and ease of access. The YAML format allows for easy parsing and manipulation by both users and computer programs. The database includes both linear and nonlinear optical properties, with the nonlinear properties (n2) being a recent addition to address the challenges of high-power lasers. The collection process involves systematic data extraction from various sources, including scientific papers, manufacturer catalogs, and online databases. Data extraction is verified through manual comparison, plot comparison, and cross-entry comparison to ensure accuracy. The database is regularly updated to incorporate new data and improvements. Users can access the database through the RefractiveIndex.INFO website or via Python scripts that facilitate data retrieval and analysis. The database is also available on GitHub, where additional scripts and tools are hosted. The dataset is publicly available under a Creative Commons Zero license, allowing unrestricted use, distribution, and modification. The *refractiveindex.info* database is an essential tool for researchers, engineers, and students working in the field of optics and photonics, providing a comprehensive and reliable source of optical constants.