The Internet revolution has driven Encyclopaedia Britannica, the onetime bastion of middle-class book shelves, to offer the entire encyclopaedia for free over the Internet.

The decision completes the transformation of the encyclopaedia - this century it has evolved from an expensive investment for the hard-backed 13-volume set sold by door-to-door salesmen, to a multimedia CD-Rom costing around £100 sterling (€155). Now it is a free "knowledge destination" for Internet users.

The move was prompted by dwindling sales, which for the printed edition peaked in 1991. In 1994, the first CD-Rom version was introduced, but its price - originally more than £400 - has been scaled back. The company now hopes that by offering its service for free, it will make money from sponsorship, advertising and e-commerce transactions related to use of the website. It hopes these revenues will compensate for the short-term sacrifice of revenues from subscription and print sales.

The Encyclopaedia Britannica has been available over the Internet since 1994 for a charge.