Phage display is a powerful tool to produce recombinant antibodies against a given antigen without animal immunization. This technology employs libraries of recombinant bacteriophages that display billions of different functional antibody fragments on their surface. They are selected by panning in vitro against the target antigen in search for specific binders. In this chapter, we describe the selection of single chain variable fragment (scFv) antibodies to be used for detection of allergenic proteins from nuts in food products. The artificial libraries TomLinson I+J (MRC Laboratory of Molecular Biology and MRC Centre for Protein Engineering) were employed that resulted in successful phage-ELISA systems for detection of almond and walnut proteins in commercial food products.