As its various collections grew, the Museum Library established itself as one of the finest international collections on natural science.
By 1900 the General Library held 19,395 volumes and 5,569 sheet maps.
The science department libraries were also well stocked:
An extremely accurate central card catalogue was created, and between 1903 and 1940 a Catalogue of the Books, Manuscripts, Maps and Drawings was published in 5 volumes and three supplements.
When Bernard Woodward retired in 1920, his successor Basil H. Soulsby (1864-1933) continued building the collections. Soulsby procured a number of obscure editions of Carl Linnaeus’ work through a project on the Catalogue of Works of Linnaeus in the British Museum.
Alexander Cockburn Townsend (1905-1964) took over from Soulsby in 1930, and evacuated most of the Library’s valuable items from London during the Second World War.
In October 1975 the Museum libraries were brought together into a unified service called the Department of Library Services, under a central management team headed by Maldwyn Jones Rowlands (1918-1995).
At this point, the Library had a staff of 42, operated 6 Reading Rooms and received nearly 8,500 visitors a year.