This study examines how material and historical authenticity are balanced with artistic unity and aesthetic legibility in the conservation of ornamental stone in Great Britain and North America through a case study analysis of recent conservation of exterior carved stonework at the 15th century Rosslyn Chapel in Roslin, Scotland and the 18th century Church of Mission San José in San Antonio, Texas. Despite their stylistic, cultural and historical differences, both buildings are significant architecturally for their intricate ornamental stonework and both have played an important role in the artistic and cultural psyche of their respective regions. Additionally, both buildings have undergone considerable alteration and decay in their lifetimes. The case study analysis reveals that, at both sites, the approaches to treating the decayed stonework are guided by the need to maintain the material authenticity of the original stonework as well as a desire to maintain the aesthetic legibility of the original design. However, the treatment program for Mission San José is more heavily influenced by a theory of artistic unity and a belief that the completeness of the original design is vital for understanding and appreciating the intent and meaning of that design. The conservators at Rosslyn Chapel are less concerned with the aesthetic legibility of the exterior carved stonework because the completeness of the details of the original design is not seen as integral for understanding the monument and its significance. Rather it is the overall integrity of the stonework that is important, not the legibility of each carved element. However, this discrepancy between the two approaches is not due to a basic difference in conservation philosophy between the two groups of professionals, but rather the differences in the nature of the ornamental stonework and the importance of the design legibility for the overall significance of the building.