Online content providers - amongst them the BBC, Channel 4, Bebo, Yahoo and Google - have all signed up to new guidelines, which are hoped will protect kids online.
The guidelines will see material flagged online, which the providers think may be unsuitable for children.
They only apply to commercially produced content and so will not affect user generated content on sites such as YouTube and Facebook.
Under the new guidelines content providers must ensure they provide information that "gives adequate information to enable the user to make an informed choice about whether or not to access the content".
Antony Walker, chief executive of the Broadband Stakeholder Group, which was behind the code's introduction explains: "Consumers want clear information to help them make more informed choices. These principles set out the underlying approach that content providers are taking so that consumers get the information they need, and in a way that makes sense to them across different media platforms".
The new content information guidelines are backed by regulator Ofcom and see existing principles of broadcast consumer guidance extended across the wider new media industry, explains The Guardian.
The mobile phone industry already self-regulates its adult content services, using age-verification technology.
The Association for Television on Demand has a code of practice for TV firms and the BBC labels programmes that may be unsuitable for young audiences on its iPlayer online service.
A lock on the iPlayer allows parents or guardians to prevent younger viewers from watching certain content.
The Broadband Stakeholder Group will review the operation of the code of conduct next year.