UniChem is large-scale non-redundant database of pointers between chemical structures and EMBL-EBI chemistry resources. Its purpose is to optimise the efficiency with which structure-based hyperlinks may be built and maintained between chemistry-based resources, and is particularly suitable for creating such links 'on the fly' (by use of REST web services).

Primarily, this service has been designed to maintain cross references between EBI chemistry resources. These include primary chemistry resources (ChEMBL, ChEBI and SureChEMBL), and other resources where the main focus is not small molecules, but which may nevertheless contain some small molecule information (eg: Gene Expression Atlas, PDBe).