Proper understanding of the pathogenesis of type I allergy relies on the identification of allergen epitopes. The phage display technique is a relatively new one to define peptide structures that mimic natural epitopes, including conformational B-cell epitopes. Peptides displayed on the phage recognized by an antiallergen antibody mimic the physicochemical properties of the amino acids and are, therefore, called mimotopes. The main advantage of the biopanning technique described in this chapter is that the structure of the antigen/allergen may be completely unknown; the only material needed is an antibody binding to it. The mimotopes generated by this technique display the features of the antigen/allergen but do not crosslink the mast cell-bound IgE-antibodies. Thus mimotopes could be used as a safe alternative to the commonly applied allergen extracts in immunotherapy of allergic patients and direct the immune response toward the desired allergen epitopes. In the selection procedure called biopanning, phages with the mimotopes best recognized by the selecting antibody are amplified. The titers of phages specifically binding to the selection antibody are checked. In this chapter we describe two alternative methods for colony screening: the immunoblot and ELISA.