Abstract: The present invention relates to the manufacture of mono, di and multivalent polypeptide binding complexes, also mono, di or multispecific polypeptide binding complexes and uses thereof. The invention also relates to the manufacture and use of a diverse repertoire of antigen specific VH binding domains derived from phage display libraries, transgenic animals or natural sources. Preferably the VH binding domains and the dimerisation domains comprise human sequences. The polypeptide binding complexes comprise homo or heterodimerisation domains with four antigen binding [VH] domains fused at the amino and carboxyl termini of the dimerisation domains preferably using natural hinge or linker peptides. Where the polypeptide binding complexes lack CH2-CH3 effector functions they are preferably less than 120 kDa in size. Routes of manufacture are described herein.