Church museums have been functioning from the first half of the nineteenth century. Their almost century-old history inclines us to further reflections - they originated in assorted periods and not always were established for the same reasons. The museums in question were subjected to various transformations produced by diverse political and economic premises. In Poland, the first Church museums were founded at a time of the loss of the country's independence. This fact directly influenced the organisation of Church museums in lands which prior to the partitions belonged to Poland. Their origin was the outcome of the necessity of extracting the property of the Polish Nation and salvaging it from devastation. Yet another factor influencing the establishment of Church museums were the unsatisfactory conditions of storing objects withdrawn from the religious cult. A characteristic example of institutions of the discussed variety is the Diocesan Museum in Plock, the first such museum in the Kingdom of Poland. Its special building, intended specifically for museum functions, was the first to be erected and to the end of the 1970s the only of its kind in Poland. It is here that the museum staff realised the postulates of the Resolution on Sacral Art issued in 1925 by Pope Pius XI, and conducted a thorough inventory of the diocese. In 1928 the museum published its Statute upon the initiative of the museum director, Rev. Alexander Dmochowski - the first and until 1937 the only such status of a Diocesan Museum in Poland. During the long history of its existence the titular museum always protected historical monuments in various ways: it safeguarded monuments withdrawn from the religious cult against the effect of the passage of time, prepared inventories of movable and immobile monuments, and made it possible to set up a scientific register of monuments of art. Such an inventory made it possible to, first and foremost, discover valuable monuments and prevent the alienation of cultural property.