在德国的城市街角、广场和郊区超市，一排排公共书架正在走入人们的视野。你可以随意取阅或贡献书籍，无须登记、没有期限，也不限册数。

Take a book, leave a book. In the birthplace of the printing press, public bookshelves are popping up across the nation on street corners, city squares and suburban¹（郊区） supermarkets.

In these free-for-all libraries, people can grab whatever they want to read, and leave behind anything they want for others. There's no need to register, no due date, and you can take or give as many as you want.

"This project is aimed at everyone who likes to read — without regard to age or education. It is open for everybody," Michael Aubermann, one of the organizers of the free book exchange in the city of Cologne, told The Associated Press.

The western city's latest public shelf, a €5,000 ($6,883) steel bookcase with acrylic（腈纶，亚克力） glass doors, was put up two weeks ago next to Bayenturm, one of the city's medieval towers. It is the fourth free shelf that Aubermann's group, the Cologne Citizen's Foundation, has placed outside; there are two more inside local Ikea outlets².

"We installed our other outdoor shelves last year and it's been working really well," said Aubermann, a 44-year-old who works in IT management.

The public book shelves, which are usually financed by donations and cared for by local volunteer groups, have popped up independently of each other in many cities across Germany including Berlin, Hannover and Bonn, and also in suburbs and villages.

Each shelf holds around 200 books and it takes about six weeks for a complete turnover³, with all the old titles replaced by new ones, he said.

Even commercial book stores and online book retailers⁴ seem to support the idea of free book exchanges.

"We see this project rather as a sales promotion⁵ than as competition," said Elmar Muether, the acting⁶ branch manager at Cologne's Mayersche Buchhandlung book store. "If books are present everywhere, it helps our business too."

Bettina Althaus, a spokeswoman for buch.de, a German online bookstore comparable to Amazon.com, also welcomed the movement.

"Public bookshelves are in no competition with the online book trade. On the contrary, we are happy about any kind of motivation to read," Althaus said.

So far, the Cologne book group has had few problems with vandalism（故意毁坏文物的行为） or other kinds of abuse, though a used-book seller once scooped⁷ up every volume on a shelf to sell at a flea⁸ market. Another time the shelves kept getting stacked with material from a religious group.

"We made sure to get rid of that stuff as quickly as possible," Aubermann said. "Propaganda is the only kind of literature we do not allow here, whether it is right-wing, racist⁹ or proselytizing¹⁰（使改变宗教信仰） ."

At another bookshelf in the Bayenthal neighborhood, the lower shelves were reserved for children's literature only.

"It is important that we make it easy for everyone to overcome their inhibitions and participate in this 'reading culture on the street' — from old readers to kids to immigrants," Aubermann said.

While most of the shelves have so far been put up in upscale neighborhoods, Aubermann and the 20 volunteers who help look after the project are planning to put up future shelves in poor neighborhoods, where residents often don't have as much access to literature.

Nobody really knows where the idea for the public shelves originally stems from. What's certain is it's a popular grass-roots movement that's catching¹¹ on — even abroad.

Just a few weeks ago, Aubermann said he was contacted by a Portuguese¹² NGO that asked him for help with opening public book shelves in poor rural areas of Mozambique.