Completions of Cathedrals were, in some cases (e.g. Sagrada Familia in Barcelona) still are large scale and unique projects which were carried out across Europe at the end of the 19th and even during the course of the 20th century. The aim of this dissertation is a comparison of the late completion of St. Vitus Cathedral in Prague (1344 - 1929) and Cologne Cathedral (1248 - 1880) on the background of the Neo-Gothic Revival, finding the elements which the cathedrals and subsequently the completions have in common. The dissertation concern is also to describe the 19th century political, religious and historical background behind the completions and the influence of the freshly established Conservation Movement. The historical comparison will include the medieval origin of building cathedrals and the religious influence on its design, the impact of French cathedral builders to the Northern and the Central Europe and the Parler's medieval master-masons family involvement in both projects as the leading late gothic builders family in the German speaking lands. The importance of Gothic drawings in the medieval times as the medium to spread the knowledge of cathedral design and also how the discovery of the very same drawings led to the successful completion. The contemporary view on larger scale projects like completions to be investigated together with analysis of the current phase of the Conservation Movement development.