Libraries of antibody fragments displayed on filamentous phages are now a widely used approach to isolate antibodies against virtually any target. We describe a simple protocol to make large and diverse libraries based on a single or a limited number of frameworks. The approach is flexible enough to be used with any antibody format, either single-chain (scFv, VHH) or multi-chain (Fv, Fab, (Fab')2), and to target in a single step the six complementarity-determining regions-or any other part-of the antibody molecule. Using this protocol, libraries larger than 1010 can be constructed in a single week.