Humanized antibodies are antibodies from non-human species whose protein sequences have been modified to increase their similarity to antibody variants produced naturally in humans. The process of "humanization" is usually applied to monoclonal antibodies developed for administration to humans (for example, antibodies developed as anti-cancer drugs). Humanization can be necessary when the process of developing a specific antibody involves generation in a non-human immune system (such as that in mice). The protein sequences of antibodies produced in this way are partially distinct from homologous antibodies occurring naturally in humans, and are therefore potentially immunogenic when administered to human patients (see also Human anti-mouse antibody). The International Nonproprietary Names of humanized antibodies end in -zumab, as in omalizumab (see Nomenclature of monoclonal antibodies).

Humanized antibodies are distinct from chimeric antibodies. The latter also have their protein sequences made more similar to human antibodies, but carry a larger stretch of non-human protein.

There are other ways to develop monoclonal antibodies. This list covers many of the monoclonals developed for use in humans.