Hematologic malignancies are predominantly treated with chemotherapy or a combination of chemotherapy with monoclonal antibodies. Current treatment regimens often are not satisfactory due to severe side effects and a substantial proportion of relapsed patients. This has prompted the development of better tolerated and more efficacious immunotherapeutic strategies for the treatment of lymphoma and leukemia. With blinatumomab (MT103) a first antibody, which can potentially engage all cytotoxic T cells of a patient for tumor cell lysis, is now available for clinical evaluation. Blinatumomab is a single-chain bispecific antibody construct with specificity for CD19 and CD3 belonging to the class of bispecific T cell engager. Here, we review the current progress in development of blinatumomab for treatment of patients with CD19-expressing hematological malignancies.