ChemSpider is a free-to-access collection of compound data from across the web, provided for the benefit of the community by the Royal Society of Chemistry (RSC). It aggregates chemical structures and their associated information into a single searchable repository and makes it available to everybody. ChemSpider builds on the collected sources by adding additional properties, related information and links back to original data sources. ChemSpider offers text and structure searching to find compounds of interest and provides unique services to improve this data by curation and annotation and to integrate it with users’ applications. ChemSpider SyntheticPages, CS|SP, extends this model to cover reactions, providing quick publication, peer review and semantic enhancement of repeatable reactions