Abstract: The present invention provides optimized nucleic acid molecules, methods for optimization of nucleic acid molecules and uses of optimized nucleic acid molecules. A modular design principle is provided that is suitable to generate a nucleic acid, particularly mRNA, which is tailored for a respective application. The nucleic acid molecules of the present invention can be obtained by the versatile combination of multiple modules on nucleic acid level. Such nucleic acid, e.g. mRNA, can be tailored by combining one or more modules, comprising (i) a nucleic acid moiety encoding a polypeptide of interest (e.g. a protein potentially producing a therapeutic outcome) and (ii) at least one further coding or non-coding nucleic acid moiety, e.g.