The effect of foreign laws on the national legal system and their penetration into it was a significant factor in the modernisation of Russia’s social and economic order (in which at the time the feudal order was still very strong). So, the question of to what degree foreign (including Roman law) legal experiences influenced Russian legislation, legal doctrine and procedural practice is a significant one. The aim of this article is to examine the effect of so-called ‘conditional testaments’, or ‘conditional testamentary dispositions’, on Russian inheritance law as a factor in its modernisation. The conditions in the will allowed people to expand the limits of the freedom of will set up by feudal prohibitions, limits that impeded the modernisation of property relations. We should stress that Russian legislators and judges referred legatum, substitution, fideicommissum to conditional testaments. Due to the predominant agrarian and patriarchal origins, the strong survival of group feudal order and the way in which Russia generally lagged behind industrially developed countries (France, Germany), Russian lawyers had to refer to foreign experience when regulating new bourgeois relations. The Russian legislature’s juridical techniques were based on the achievements of Roman and foreign law. Foreign legal influence penetrated legislative practices and legal procedures because Russian lawyers mainly got their education studying Roman law and foreign legislation. Russian scientists, judges, senators, etc., constantly expressed their respect for Roman law, Roman juridical experience and contemporary legal science, especially that of Germany.