This protocol describes the design and development of recombinant monovalent antigen-binding molecules derived from monoclonal antibodies through rapid identification and cloning of the functional variable heavy (VH) and variable light (VL) genes and the design and cloning of a synthetic DNA sequence optimized for expression in recombinant bacteria. Typically, monoclonal antibodies are obtained from mouse hybridomas, which most often result from the fusion of B lymphocytes from immunized mice with murine myeloma cells. The protocol described here has previously been exploited for the successful development of multiple antibody-based molecules targeting a wide range of biomolecular targets. The protocol is accessible for research groups who may not be specialized in this area, and should permit the straightforward reverse engineering of functional, recombinant antigen-binding molecules from hybridoma cells secreting functional IgGs within 50 working days. Furthermore, convenient strategies for purification of antibody fragments are described.