The article constitutes an analysis of the publication of Lithuanian historians from the years 1988–2009 and the hitherto unpublished Encyclopedia of the Grand Duchy of Lithuania. The Union of Horodlo was not the subject of separate research; it was incorporated into discursive writings on Polish-Lithuanian relations. Originally, it was presented in a traditional and ambiguous manner – underlining both the advantages and disadvantages of the union for Lithuania. The Union of Horodlo was properly presented in the academic synthesis of the history of Lithuanian up until 1795 written in 1998. However, the only fragment which expresses any reservations is the one which criticises the Polish-Lithuanian rapprochement, the result of which was the Union of Lublin in 1569, also perceived negatively. Other publications such as the syntheses of E. Gudavičius and M. Jučas generate considerable doubts due to the fact that the interpretation of facts is given priority over their presentation; moreover, the judgments presented in those books are biased. Recent years have welcomed important changes in contemporary Lithuanian historiography, an example of which is a multi-volume synthesis of the history of Lithuania (vol. 4 of 2009) and encyclopaedic entries to the previously mentioned Encyclopedia of the Grand Duchy of Lithuania. Th e works are based on the concept of the so called “compound monarchy” – the term of “the Crown of the Polish Kingdom” which is well known in Polish historiography. It explains contradictions on the acts of the Union of Horodlo between the act of incorporation of Lithuania into Poland and Lithuanian’s self-determination. Also new is a positive evaluation of the Union of Horodlo, which had been absent in Lithuanian historiography so far.