Nowadays, growing problem is the greater amount of concubinage. Should consider this as a problem for this reason that these compounds are legal, although not as stable as marriages, moreover not provide family security in the highest degree. In Polish law there is no law on concubinage and the current legislation doesn’t have this concept. Often can be found stating that Polish law disqualifies persons in informal relationships, and the best solution would be the adoption of the Law on concubinage. In this paper, the author demonstrates that the law does not ignore completely the above-mentioned persons and refers to them by the use of terms such as “person close up” or “closest person”. There is a  noticeable change in the law in the direction of opening up the compounds include informal through the introduction of the above terms. The literature indicates that concubinage and cohabitation are not identical concepts, for the purpose of work (the purpose of which is to show the legal effects of compounds other than the permanent marriage), however, the author agrees with the position that commonly these terms can be used interchangeably. Due to the inability to identify all existing legal consequences of cohabitation, reference is made only to some of them, to demonstrate that such compounds are not overlooked by law. The analysis discussed issues proved to be helpful not only literature and case law, but also statistics showing, among others, the difference in the number of people staying in cohabitation in 2002 and 2011.