CELSG is a cooperative network of investigators and clinical institutions in Central and Eastern Europe that has been formed to conduct clinical trials in the field of chronic myelo- and lymphoproliferative diseases according to Good Clinical Practice guidlines. The ultimate goal of CELSG is to enhance the standard of care for chronic hematological malignancies by developing innovative diagnostic and therapeutic approaches and testing increasingly more effective therapeutic strategies. To date CELSG had a strong clinical resrrach focus on chrnic myelogenous leukaemia. In the upcoming years CELSG will expand its clinical trial portfolio to other myeloproliferative disorders and chronic lymphocytic leukaemia.