The development, scope, and functionality of the Web-based ionic liquids database, ILThermo, are described. The database is available free to the public and aims to provide users worldwide with up to date information from publications of experimental thermophysical properties for ionic liquids, including numerical property values, measurement methods, sample purities, purification methods, and uncertainties. The database can be searched in terms of the ions constituting the ionic liquids, the ionic liquids themselves, and their properties and through literature citation information.