title SUMMARY /title Thomas Henry Court (1868-1951) played an important role in the growth of the collection of scientific instruments in the Science Museum in South Kensington. This led to the formation of a file in the museum's official registry ('The Court file'). Of Court's own documentation and papers on instruments, the bulk was passed on to the microscope collector Harold Heywood, but some came into the museum's possession, probably together with his instruments. In 1979 and 1992, respectively, these two groups of documents were deposited in the Science Museum Library ('The Court archive'). This article discusses Court's activities and assesses the value of these documents as a source of information on the growth of interest in antique scientific instruments and their makers during the first half of the twentieth century.