The following summarises the main rules affecting Domain Name registrations for Top Level (.com etc) and UK (.co.uk etc) domains. These notes should be used for guidance only as rules do change! The ultimate authority on these rules is the appropriate naming body.

Top Level Domain (TLD) Names

Names can only contain the following characters:-
a b c d e f g h i j k l m n o p q r s t u v w x y z - 0 1 2 3 4 5 6 7 8 9
Spaces are not allowed and names may be a maximum of 63 characters excluding the extension eg '.com'.
Names must be at least 3 characters long eg abc.com

NOTES 
The .com, .info, .name, .net, and .org TLDs are open and unrestricted. Traditionally, however, names in .net have been used by organisations involved in Internet infrastructure activities and .org is frequently used by noncommercial organizations. .biz is reserved for use by businesses. .name is dedicated exclusively to individuals' personal names and must be of the format firstname.lastname.name eg fred.flintstone.name

UK Domain Names

Registration of all UK domain names are subject to Nominets Terms and Conditions

NOTES
 me.uk is intended for personal use. They are expected to be made for natural persons, such as Mr John Doe registering johndoe.me.uk.

To register the .ltd.uk and .plc.uk names your company MUST be a UK limited company or public limited company respectively. The name registered must be EXACTLY the same as registered at Companies House. White space between words shall either be ignored or replaced by a single hyphen "-". For example 'First Class Software Ltd' may register either first-class-software.ltd.uk or firstclasssoftware.ltd.uk. You will need to include the Company Registration Number in your application.

CentralNIC Domain Names

CentralNic (previously known as Nomination) provides a wide range of alternative domain names. These are not ICANN-approved and so there are no local rules to qualify for these domain names.