In recent years, there has been growing interest in the creation of synthetic proteins with perfect internal symmetry. Such structures can be achieved by analysing the consensus sequences of natural proteins or de novo by computational methods. Proteins with translational (polar) symmetry have found applications as artificial antibodies, while those with point (cyclic) symmetry have proved stimulating models of molecular evolution. Proteins with internal repeats can also serve as building blocks for the creation of larger symmetrical assemblies, such as cages, that may depend on and mutually organise other molecules. This has been demonstrated by the biomineralisation of the smallest nanocrystal in a designer protein complex.