On 1 March the newly established European Reference Networks (ERNs) will start their work. ERNs are unique and innovative cross-border cooperation platforms between specialists for the diagnosis and treatment of rare or low prevalence complex diseases. 24 thematic ERNs, gathering over 900 highly specialised healthcare units from 26 countries, will begin working together on a wide range of issues, from bone disorders to haematological diseases, from paediatric cancer to immunodeficiency. Joining up of EU's best expertise on this scale should benefit every year thousands of patients with diseases requiring a particular concentration of highly specialised healthcare in medical domains where the expertise is rare. ec.europa.eu/health/ern.