Targeting cancer cells with monoclonal antibodies has become an indispensable part of modern treatment against hematologic malignancies. The excitement of the first successful experimental results could be confirmed by large multicenter trials, thus paving the way for new approaches in first-line, relapse, and maintenance therapy. Three antibodies--rituximab, 90Y-ibritumomab tiuxetan, and alemtuzumab--are in clinical use worldwide and are reviewed in this chapter with a focus on practical information and fundamental principles of antibody-based therapy.