In the Russian social and political thought there is a tradition of thinking about the universal fraternity. The important role for the creation of this tradition was played by the philosopher Nikolay Fedorov. The aim of the article is to depict the sources and the evolution of the idea of fraternity. The author analyzed a number of texts created by the Russian thinkers of the XIX and XX centuries where different levels of interpreting the ideal of fraternity are given. The ideal mentioned goes back to the Sergius' Trinity image: active and religious interpretation of fraternity which encourages everybody to unite in multiunity similar to the divine tripersonality. Besides, there is a philosophical and ethic interpretation which states that all people's unity has an absolute moral value. The natural-scientific interpretation also postulates the highest value of fraternity and solidarity on the basis of belief in "deep natural laws". And the specific and applied interpretation of the idea of fraternity assumes that the principles of fraternal life can be embodied into practice.