This chapter introduces the nonimmunologist to methods used to produce mouse monoclonal antibodies. Antibodies are produced by animals’s B-cells or B-lymphocytes. The B-cells can be found in the spleen, lymph nodes, Peyer's patches of the digestive tract, and peripheral blood. The mouse monoclonal antibody production protocols that follow are modifications of the procedures published by Van Deussen and C. A. Whetstone. The two things to consider with respect to antigen preparation are antigen purity and immunogenicity. Large antigens with highly repetitive epitopes exposed on the surface of the molecule are usually more immunogenic than smaller antigens with fewer repetitive and buried epitopes. Two different schemes can be used to stimulate B-cell antibody production. These schemes are referred to as in vivo immunization and in vitro B-cell antigenic stimulation. Before the cell fusion protocol can be performed, the spleen should have been surgically removed from the mouse, and the spleen cells should have been extracted from the spleen.