The basis of European communities’ integration is diversified. Some of its aspects are particularly emphasized, like the dynamics of economic development, which creates new quality of life for millions of Europeans. Much attention is devoted to the common historical past and the common democratic political values. The attention is focused, to a lesser extent, on what constitutes the real basis of cultural identity for European societies, namely law and the attitude to it. It is law and values attributed to it as well as legal institutions, which have been the strongest links of cultural chain connecting Europeans. Except for a basic issue, that is the Roman law tradition, one can point at a great common achievement with essential practical qualities. Lex mercatoria in the field of commercial law. Traditions of European constitutionalism, including the second, in the terms of the time of creation, modern constitution which was Polish constitution of 1791. Modern civil law becoming widespread due to the French Napoleonic Civil Code, which at the beginning of the 19th century was binding on the eastern European territory within such borders, which are now the European Union’s borders. The exchange of ideas and legal doctrine from the Middle Ages at European Universities. Promoting in these discussions, starting from the 16th century, modern solutions in the area of law, like the postulate of departing from capital punishment and equal rights. A systematic development of subjective rights, human rights, equal rights for women, rights of minorities and rights of the disabled. Introducing these rights to the positive law and ensuring their international and institutional protection.