A study of category of legitimate interest in law has a value for its application in practice in various areas of law. At all stages of the of research of legitimate interest, scientists have considered this category by category of interest. These categories relate to each other as a private and common. During the research a legitimate interest in the law the author identifies three periods: the pre-Soviet (the end of XIX century until 1917); Soviet (1917—1990 years); Post-Soviet (from 1990 to present). The legitimate interest was examined by the researchers in a broad sense as the target of subject which it seeks to achieve, and in a narrow sense — as a legal mean. Category of legitimate interest remains the same no matter in what area is its implementation. Legitimate interest provides only the subjects’ desire that is not contrary to law and is within the scope of legal regulation. Relevant to the present time in the scientific studies is that they point out the need for protection of the legitimate interests on a par with the subjective rights.