More than 150,000 historic books from 160 National Trust properties have been catalogued online for the first time.
The collection, which includes 17th century atlases from Dunham Massey country estate in Cheshire to a rare library of miniature books for children held at the property A La Ronde, in Devon, provides instant access to information for scholars and members of the public.
Browsers will be able to see which books are in the Trust's collections as well as where each comes from, how it is bound and who it belonged to.
Notes alongside those featured online also provide information about the life of the book's owner where known and the property where it ended up.
Work on the cataloguing project, which began in 1958, was largely carried out in the last 12 years with more than half of this taking place within the last five.
But the Herculean task remains to be completed - Trust staff and contractors have another 70,000 books still to catalogue.
Mark Purcell, the National Trust's Libraries curator, said their efforts meant the collection was now available to a much wider audience.
"This project represents an exciting and important step forward in making our book collection more accessible to historians, researchers and students, providing information about, and improving access where possible, to the books in our collections," he said.
"But it also offers a useful and flexible resource for property staff and volunteers, by helping them to unlock their collections for new and changing displays, and thereby increasing visitor interest and enjoyment.
"One such example is the spectacular Caxton Missal at Lyme Park in Cheshire. This rare 15th century liturgical book is on display alongside 'touch screen' technology that has been wowing visitors and enabling them to 'turn' its pages."
Among the Trust's diverse collections are copies of almost all the major editions of the Bible printed since 1475 in Blickling Hall in Norfolk.
The "remarkable" library of a yeoman farmer at Townend in Cumbria can also be found alongside the private library of writer Rudyard Kipling at Batemans, a 17th century Jacobean house in Sussex where he once lived and at the Wimpole estate in Cambridgeshire.
Other highlights include the only copy of the earliest known English ABC, circa 1535, (Lanhydrock, Cornwall); The Crafty Chambermaid's Garland, 1771 - a bawdy ballad for north country farmers (Townend, Cumbria) and the Bible supposedly used by Charles I on the scaffold (Chastleton House, Oxfordshire).
The catalogue can be found at http://copac.ac.uk/libraries/nationaltrust.html .