ChemSpider was developed with the intention of aggregating and indexing available sources of chemical structures and their associated information into a single searchable repository and making it available to everybody, at no charge. There are many tens of chemical structure databases such as literature data, chemical vendor catalogs, molecular properties, environmental data, toxicity data, analytical data etc. and no single way to search across them. Despite the diversity of databases available online their inherent quality, accuracy and completeness is lacking in many regards. ChemSpider was established to provide a platform whereby the chemistry community could contribute to cleaning up the data, improving the quality of data online and expanding the information available to include data such as reaction syntheses, analytical data and experimental properties. ChemSpider has now grown into a database of well over 20 million chemical substances integrated with over 300 disparate data sources, many of these directly supporting the Life Sciences. This presentation will provide an overview of our efforts to improve the quality of data online, to provide a foundation for the semantic web for chemistry and to provide access to a set online tools and services to support access to these data. I will also discuss how ChemSpider is being used to enhance Semantic Publishing in Chemistry at RSC.