Since the beginning of the 1970s, there has been a broad development in the direction, where the nucleus is treated as a relativistic system. Many new, important results have been obtained in this field during the last 30 years. In particular, it has been established that the anomalously large spin—orbit coupling in nuclei, which is treated purely phenomenologically in the nonrelativistic framework, can be explained naturally in the relativistic approach. Also, pseudospin symmetry has been the subject of many investigations, for both spherical and deformed nuclei. Recently it has been understood that the notion of pseudospin has deep roots in the relativistic theory.