Formed in March 2024, the Working Group aims to extend our knowledge of patients with very rare coagulation factor deficiencies with focus on demographics, clinical bleeding phenotype, laboratory phenotype, genotype characterization, treatment strategy and quality of life; to improve health care, concerning diagnosis, genetic counseling and treatment in patients with very rare coagulation factor deficiencies; to define research priorities with the aim to reach all areas in Europe, independent of the socio-economic background; and to facilitate educational sessions for the broad audience of the EAHAD.