Most British citizens may travel to the United States without a visa, under the Visa Waiver Program (VWP). Qualifying citizens of the UK or of one of the 35 other countries in the VWP may travel to the US by air or sea on a participating carrier or authorized private aircraft with just a qualifying passport and an onward/return ticket.  Upon completion of online ESTA registration and the green I-94W form, and inspection by Customs and Border Protection (CBP), VWP travelers may be admitted for stays up to 90 days. (Slightly different requirements apply to persons arriving by land.)   Every year an average of 12.6 million travelers enter the US visa-free in this way.

To use the VWP you must ensure that you satisfy requirements relating to (1) your passport, (2) the activities you intend to undertake in the US, and (3) your personal history.  If you do not meet the qualifications in all three categories, you must obtain a visa for US travel.    

As of January 12, 2009 there is a further requirement:  (4) you must have registered on the new ‘Electronic System for Travel Authorization’(‘ESTA’) before you travel. 

1. Passport
   All VWP travelers regardless of age must have an individual, machine-readable passport. Such passports have two lines of coded text at the bottom of the photograph page. To ensure that your passport is machine-readable you may wish to compare it against the example on the Department of State’s website.
   Passports must be valid for six months beyond the date the traveler will exit the U.S., however, the U.S. has signed agreements with a number of countries to waive this requirement. For a list of such countries click here. When such an agreement is in place, the passport must be valid for the entire period of the visitor's intended stay.
   
   The additional requirements for VWP-eligible passports are as follows:
   
   

   1. If your passport was issued before 26 October 2005, and is machine-readable, it is valid for VWP travel.
   2. If your passport was issued between 26 October 2005 and 25 October 2006, and is machine-readable, it will be valid for VWP travel if it contains a digital photograph—that is, one that is printed on the passport page, not glued or laminated. 
   3. If your passport was issued on or after 26 October 2006 it is valid for VWP travel only if it is an ‘e-passport,’ containing an electronic chip storing biographic and biometric information. (On 24 July 2006 the  Identity and Passport Service announced that all UK passports issued after 5 October 2006 will be e-passports.)
   4. An e-passport is required for VWP travel if you are travelling on a passport from one of the following newly-added VWP countries:  Czech Republic, Estonia, Greece, Hungary, Latvia, Lithuania, Malta, Slovak Republic, and South Korea.
      
      
2. Activities to Be Undertaken in the United States
   
   VWP travelers may apply for admission as either visitors for pleasure or for business, and will find their passports stamped ‘WT’ or ‘WB,’ respectively.
   
   WT visitors may use their 90 days’ admission to holiday in the United States, visit family and friends, or seek medical treatment. Employment is never authorised.
   
   Persons admitted as WB visitors may conduct business activities such as negotiating contracts, engaging in litigation, or attending business meetings or conferences. With few exceptions WB visitors may not legally engage in local employment or ordinary labor for hire, and may not receive from a US source any remuneration other than expenses incidental to their visit. You will need an employment-authorised visa to undertake activities such as managing a US office or supervising employees; providing consultancy services in the US beyond mere fact gathering; or soliciting clients for a US business.
   
   
3. Personal History
   
   Even if your passport and planned activities in the US qualify for the VWP, you will be ineligible to use the program if any of the following is true:
   
   

   1. You ever violated the terms of the VWP, such as overstaying on a previous entry;
   2. You were ever removed or deported from the US;
   3. You are inadmissible to the United States for any of a variety of reasons, including but not limited to
      1. You have a communicable disease of public health significance; or
      2. You have been convicted of a crime involving moral turpitude or a controlled substance violation (there are exceptions).

   If any of these statements is true you must obtain a visa before traveling to the United States.  Also,  ‘yes’ answers to any of the questions on the reverse of the I-94W will lead to increased questioning at the port of entry, although they may not of themselves disqualify you from using the VWP. The U.S. Embassy, London advises on its web site that anyone who has ever been arrested must apply for a visa. On this topic you may wish to check the Embassy’s Visa Waiver Wizard.

4. Electronic System for Travel Authorization (‘ESTA’).
   
   As of January 12, 2009 potential travelers are required to provide electronically via ESTA the same information currently required on the Form I-94W, consisting of biographical data and answers to eligibility questions regarding, for example, arrests and convictions for certain crimes, visa revocation or deportation, and communicable diseases. This will be done by logging into a dedicated website:  https://esta.cbp.dhs.gov. DHS recommends that travelers submit this information a minimum of 72 hours in advance of departure but claims that the system will be able to accommodate emergency travel on less than 72 hours’ notice.
   
   Each travel authorization under ESTA is valid for up to two years, depending upon the expiry date of the traveler’s passport. However, a VWP traveler must obtain a new ESTA authorization if he or she is issued a new passport, changes his or her name, gender, or country of citizenship. In addition, a traveler must obtain a new ESTA authorization if any answer to the ESTA application eligibility questions changes.
   
   Finally, remember:  If you cannot use the VWP, all is not lost. B1/B2 visitor visas for UK citizens can be valid for multiple entries and for up to 10 years. Even if an immigration or criminal law violation makes you ineligible for a visa, waivers of ineligibility are often available. In such cases, too complex to be treated in this brief article, the legal advice of a qualified US immigration lawyer should be sought. For information on ineligibilities and waivers of ineligibilities, see our article Washington, we have a problem! Ineligibilities and waivers.