Visitors to the UK can apply for a General Visitor visa if they meet certain criteria, as stated by GOV.UK. The trip must be for pleasure, and the applicant must live outside the European Economic Area or Switzerland.
Applications for General Visitor visas are also accepted for travelers visiting friends or family who are not residents of the UK or are donating an organ to a relative or friend, according to Gov.UK. Applicants must be 18 or over, be able to financially support themselves while they are in the UK and pay for a return or continuing trip. The applicant must not be in transit to a country other than Ireland, Isle of Man or Channel Islands. An application for a long-term General Visit visa also requires proof of a consistent and ongoing need to be in the UK, and that the need is not likely to change during the term the visa is valid. The applicant must also plan to leave the UK at the end of each visit.
A United States citizen planning a business or pleasure visit of 180 days or less is not required to apply for a visa, as stated by VisaHQ.com. A passport valid for at least 90 days after the visit is sufficient.