The paper presents an analysis of the heritage of the great German jurist, historian and philologist Theodor Mommsen as well as his contribution to the modern science of Roman law. The author notes that in spite of the recognition Mommsen has won in Russia, his major works Romisches Staatsrecht and Romisches Strafrecht are still underestimated in the field of jurisprudence. Mommsen's brief biography shows that in spite of the daunting bulk of his heritage he was by no means an armchair scholar, but a lively, humanely delicate and searching man, a true patriot and animal politicum, as he would call himself, grieving for his motherland. Fundamental qualities of his major work and some of its peculiarities are treated here as well. It is stressed that the system of Roman public law as it was reconstructed by him became predominant in modern historiography and has retained its authority up to now. The main principle of his system is the famous Roman principle Res publica res populi est (Cic. De rep. I. 39). The author then gives a short characteristic of Mommsen's Romisches Strafrecht and of his scientific edition of Iustiniani Digesta. He concludes that the absence of a Russian translation of Mommsen's major juridical works is a serious obstacle for developing modern historical science of law.