Copyright holders say that linking is a form of contributory infringement of copyright. This view was attacked by the court in a case involving the company Ticketmaster on the grounds that hyperlinking does not actually involve the making of a copy. Some believe that a restriction on the use of hyperlinks could be seen as a violation of the First Amendment on freedom of speech in addition to being an unworkable restriction on the operation of the internet.
The crux of the issue appears to be at what point hyperlinking ought to be taken to be an infringement of copyright. One argument is that the links should not lead to liability unless a person is benefiting economically from the link. Even if such a person does profit, there is no guidance on how to calculate what they should pay to the copyright holder.
In the UK, it is not clear whether linking from one web site to another web site infringes copyright in the linked web site. Ideally, you should ensure that, if you wish to include a link to another web site, you have permission from the owner of the web site to do so.
This may not always be practical. For further information, see our guide on Branding and Intellectual Property.