The aim of the issue is to describe and explain the importance of the chemokine system in hematology. The chemokine system is probably important for many aspects of normal as well as malignant hematopoiesis. A major focus is the development and treatment of hematologic malignancies, including the immunobiology of stem cell transplantation. The present reviews illustrate that chemokines can be involved in leukemogenesis. The chemokine system is also important both for the crosstalk between malignant cells and their neighbouring nonmalignant stromal cells (including endothelial cells) as well as for immunoregulation in patients treated with allogeneic stem cell transplantation. Thus, chemokines are important both for the pathogenesis and treatment of hematological diseases.