What is involved in being able to travel from the UK (England) to the USA?

My friend would like to visit me in the USA, but he lives in England. We would like to know the details involved in being allowed to visit here. Does he need a passport? What is a visa for? Does he need a notarized invitation to come to the states?
I would really love to have the details, or a web address giving all the details, as soon as you can get them to me. Thank you

He needs his UK passport (if he is UK citizen), which needs to be machine readable. No visa needed if staying less than 3 months (Visa waiver program). No need for any invitation, just a return airline ticket. If not UK citizen, but EU citizen, same story. If not EU citizen, he might need indeed a visa depending on country he is citizen from. The following US immigration website gives details on which country needs what: http://travel.state.gov/visa
When visa is needed, then indeed invitation letters might be needed as well, proof of sufficient funds, etc.. The website says it all. Good luck

For a British or an EU citizen to visit the United States all they need is a British or European passport for entry under the visa waiver program (vwp).

There are requirements however to traveling visa free:

- Their passport must be machine readable.

- They must not have committed an offense that resulted in either an arrest and/or conviction (including minor traffic offenses).

- Their stay must not exceed 90 days (3 months).

- They must hold either an onward or return ticket.

If the person in question does not meet any or all of these requirements then they must apply for tourist (B-2) visa in their home country. For U.K. citizens that is the American Embassy in London. (See the website below for more information regarding the B-2 visa).

So all your friend as to do if they meet the requirements is buy a round-trip ticket to America and turn up at the airport with them and their passport.

If he is British, he needs a valid British passport and a return air ticket.