This invention relates to novel monoclonal antibodies that specifically bind to the alpha-folate receptor. In some embodiments, the antibodies inhibit a biological activity of folate receptor-α (FR-α). The antibodies are useful in the treatment of certain cancers, particularly cancers that have increased cell surface expression of the alpha-folate receptor (“FR-α”), such as ovarian, breast, renal, colorectal, lung, endometrial, or brain cancer. The invention also relates to cells expressing the monoclonal antibodies, antibody derivatives, such as chimeric and humanized monoclonal antibodies, antibody fragments, and methods of detecting and treating cancer using the antibodies, derivatives, and fragments.