Diabodies are bispecific antibody fragments that have two antigen binding Fv domains. They are unique among hundreds of different formats of bispecific antibodies because they are small and rigid enough to be crystallized. Diabodies are generated by connecting variable regions of heavy and light chains by a peptide linker. Because of the short length of the linker, intramolecular association of the variable regions is not allowed. Instead, the variable regions from the different peptide chains associate together, forming a dimeric complex with two antigen binding sites. Previous crystallographic studies of diabodies demonstrate the extraordinary structural diversity of diabodies. They have also shown that the relative orientation and interaction of the two Fv domains in diabodies have substantial flexibility due to instability of the Fv interface. Introduction of site specific mutations and disulfide bridges can reduce flexibility and therefore increase rigidity and predictability of the diabody structures. These stabilized diabodies will be useful for future application to structural biology and protein nanotechnology.