Humanization is important for reducing the immunogenicity of monoclonal antibodies derived from xenogeneic sources (commonly rodent) and for improving their activation of the human immune system. Since the development of the hybridoma technology, a large number of rodent monoclonal antibodies with specificity for antigens of therapeutic interest have been generated and characterized. Rodent antibodies are highly immunogenic in humans, which limits their clinical applications, especially when repeated administration is required. Importantly, they are rapidly removed from circulation and can cause systemic inflammatory effects as well. As a means of circumventing these problems, we have developed three antibody humanization strategies that can preserve the specificity and affinity of the antibody toward the antigen whereas significantly or completely eliminate the immunogenicity of the antibody in humans. The first approach is CDR grafting and the second is chain shuffling. These two methods are all based on phage display of humanized scFv variants and selection of high-affinity humanized binders through bio-panning. The third method, humanized IgG library screening, is somehow unique. We will make a library of humanized whole IgG to be displayed on the surface of mammalian cells and then high affinity binders will be sorted by FACS.