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.
Transit ETA is only required if you pass through border control.
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