People on holiday or visiting friends will benefit from the scheme
Millions of book lovers can now borrow items from a public library regardless of where they live, under a new scheme.
More than 4,000 libraries in England, Wales and Northern Ireland are in the Society of Chief Librarians initiative.
Existing membership cards or a proof of address will allow people to use any library in the scheme, although books have to be returned to the same area.
"It's to say to people, wherever you are, you can use a library," the society's chairman Fiona Williams said.
The aim is to encourage more people to use libraries, in the face of competition from online book sellers and people browsing in bookshops with coffee bars.
Among those who might benefit from the scheme are people who need extra reading material while on holiday.
Ms Williams said: "I've just been on holiday and am into photography.
"I needed a book on Photoshop, so I went into the local library, showed my library card and that enabled me to use the library there."
She said it might also be useful for parents with children who are keen readers but who do not want to take lots of books away on holiday with them.
People will also be able to use other library services such as DVD rental and online resources, she added.
Ms Williams said: "Libraries are a public service for everybody. We want people to know that all libraries are open to them, not only the libraries where they live.
"This is an important step towards making libraries even more accessible to all."
The society is developing a scheme for the future where one library card would allow the holder to borrow and return books to any public library in England, Wales and Northern Ireland.
Scotland is not included in the scheme as its libraries are represented by a separate body, the Scottish Library and Information Council, but some libraries are considering joining the initiative.
Some areas of the UK, including the north-west of England, have already done away with asking for forms of ID for membership completely, including libraries in the Stockport, Blackpool and Manchester areas.
David Fay, libraries manager for Newcastle city council says the scheme means people who live in one area but work in another can use the facilities in either area.
"It opens up a fantastic library network nationally for everybody, so we're really excited about it," he told the BBC.
The author and former children's laureate, Michael Rosen, welcomed the move, saying borrowing should be made easier for children.
"I don't understand why when kids arrive at school, they're not given a library card and told what's available."
"Every single child in this country is entitled to at least 10, usually 12 books on one ticket. We have free books in this country, and there are I think hundreds of thousands of parents, in my experience, who don't actually know that."
The Department for Culture, Media and Sport (DCMS) welcomed the initiative, saying the government's library review due out later this Autumn will "bring the library service into the 21st century".
Plans include letting readers order books online - which would then be delivered by post, with prepaid envelopes to return them. The DCMS says it wants to make libraries more like successful bookshops, with cafes and a wider range of activities.
"We want to make them comfortable and interesting, as opposed to the often fusty image most libraries have," said a spokesman.