Brands and celebrities can prevent their names from being hijacked by porn websites before the launch of the .xxx web domain.
The suffix, which will be used by adult entertainment websites, will make it easier to find or avoid sexually explicit material online. It will create a virtual red light district.
Companies and individuals who do not want their name to be seized by an adult entertainment website can pay a one-off fee of £100 to £300.
Meanwhile, adult entertainment websites can now apply for particular web domains.
If there is conflict over matching names, this will go through an arbitration process.
Jerry Barnet, chairman of the Adult Industry Trade Association, told the BBC: "I have mixed feeling about it," he told BBC News. "From the industry and freedom of speech point of view, I'm concerned that pro-censorship and morality campaigners will use this as an excuse to try and introduce some form of censorship.
"But from a business point of view it's kind of good for us because there are new names available, and that makes branding and site naming more interesting."
