By exploiting programmable, sequence-dependent base-pairing interactions it is possible to design and build three-dimensional DNA scaffolds, to attach molecular components to them with sub-nanometre precision – and then to make them move. I shall describe our work on autonomous, biomimetic molecular motors powered by chemical fuels, hybrid DNA-kinesin devices, motors that compute, nanostructure assembly, and the use of synthetic molecular machinery to control covalent chemical synthesis.