How It Works
A United Kingdom Electronic Travel Authority or ETA is an electronically stored authority for travel to United Kingdom for short-term Tourist, Business, Visit Family or Friends, Short Term Study(courses up to 6 months), Paid Permitted Engagement(must be done in the first 30 days of your visit) travel for U.S. citizens plus 51 other nationalities.
Each person must do a separate application.
If you need to travel soon you must apply for an ETA before you travel to the UK. You can travel to the UK while waiting for a decision.
An ETA does guarantee entry to the UK. You still need to either, see a border force officer or use an ePassport gate if you are eligible.
You cannot:
Stay in the UK for longer than 6 months
Do paid or unpaid work for a UK company or as a self-employed person, unless you are doing a permitted paid engagement or event or work on the Creative Worker visa concession.
Claim Public Funds (benefits)
Live in the UK through frequent or succesive visits.
Marry or register a civil partnership, or give notice of marriage or civil partnership - you will need to apply for a Marriage Visitor visa