The recent achievements in domain nanotechnology in single crystals of lithium niobate and lithium tantalate family have been reviewed. The formation of nanoscale domain structures has been studied with high spatial resolution using modern experimental methods of domain visualization. Criteria of the investigated ferroelectric material selection and recent experimental achievements have been presented. The physical basis of the nanodomain engineering based on the role of nanoscale domains in formation of the domain patterns in highly non-equilibrium switching conditions has been discussed. The obtained knowledge allows us to manufacture the highly efficient periodically poled crystals for laser light frequency conversion.