The here described invention discloses a combination of a top and bottom loop binder library using the CD and the FG loops of a number of FnIII domains (FnIII) (e.g., FnIII7, FnIII10 and FnIII14) together with the surface exposed residues of the beta-sheet. The invention also pertains to a method of forming a library of FnIII domain polypeptides useful in screening for the presence of one or more polypeptides having a selected binding or enzymatic activity.