Words of love that span the centuries.
Written in Norfolk more than 500 years ago, the love letter will be on show to the public for the first time next month as part of an exhibition celebrating 1,000 years of English literature.
It was originally bought by the library as part of a collection of papers from a family called Paston in the 1930s, but was only rediscovered last year when the new display's curator, Dr Chris Fletcher, was looking for exhibits.
A library spokesman said that, while the language used may have changed, the sentiments expressed in the message would find sympathy with many people living today.
He said: "While technology may have changed beyond recognition since medieval times, it seems some things remain the same.
The Valentine message, which dates back to 1477, is from Margery Brews to her fiance, John Paston.
In it, she tells John she has asked her mother to put pressure on her father to increase her dowry, while saying that, if he loves her, he should be prepared to marry her anyway.
The message starts: "Unto my right well-beloved Valentine John Paston, squire, be this bill delivered.
"Right reverent and worshipful and my right well-beloved Valentine, I recommend me unto you full heartedly, desiring to hear of your welfare, which I beseech Almighty God long for to preserve."