Monoclonal antibody (mAb) therapy has been facilitated by a number of technologic advances over the past 30 years. Whereas hybridoma development of murine mAbs was requisite for the development of mAbs as drugs, the inherent immunogenicity of rodent sequences in humans has presented obstacles to the clinical application of mAbs. Sensitization to mAb therapeutics poses significant risk to the patient and may blunt the efficacy of these therapies. The advent of chimeric antibodies lessened but did not eliminate the rodent content of mAbs; thus, immunogenicity remained a concern. Further elimination of rodent sequences enabled the production of humanized mAbs, followed by current technology using phage display and, finally, transgenic mice technology, which allows for the generation of fully human therapeutic mAbs. The reduced immunogenicity of this new generation of mAbs is expected to enhance efficacy, safety, and ease of use. In addition to providing replacements for existing mAb drugs, new technologies have greatly facilitated the optimization and modification of mAbs, opening numerous therapeutic avenues.