Cancer arises when any given body cell starts to divide in places and at times at which this is not desirable. The abnormal cell grows out of control and has a selective advantage over its neighbors, thereby forming a tumor. The aberrant growth in most tissues results in the formation of a solid tumor. However, tumors originating in blood and bone marrow do not have a centralized location and are called ‘liquid’ tumors or blood cancer.  Leukemia is a cancer of the blood and the bone marrow. Acute leukemia arises in a hematopoietic precursor cell in the bone marrow. Depending on the nature of the originating leukemic stem cell, acute lymphoid and acute myeloid leukemia are distinguished. Chronic leukemia can originate in the blood or the bone marrow. Also here, chronic myeloid and chronic lymphoid leukemia exist. Multiple myeloma and lymphoma are other hematological malignancies. Within CRIG, both adult and childhood blood cancers are intensively studied.