To produce Fab libraries which are valuable supply sources of antibodies for many several targets and act important functions in discovery and identification of targets in the field of functional genomic research.

There are provided Fab libraries and methods for providing antibodies to the targets by using the Fab libraries. The Fab library contains at least 109 different Fabs and in some embodiment, contains at least 1010 different Fabs. The Fab libraries are used to isolate polyclonal Fabs or monoclonal Fabs that bind with high specificity to targets. Polynucleotides encoding the Fab libraries, Fab libraries, design and construction of the Fab libraries and methods of selection from the Fab libraries are provided.