If you’re planning to travel to the United Kingdom anytime soon, a travel caution: Effective January 8th, any U.S. citizen landing at a U.K. airport will need an E.T.A — otherwise known as an Electronic Travel Authorization.

And you’ll need to get this E.T.A. before you depart the U.S. You can apply online, and it costs under $13.

Once it’s approved, it’s valid for two years and good for multiple entries of up to six months in Great Britain.

Any travel agent can help with this, but the important caution once again: you need to get this before you depart, and since the process could take up to 72 hours to complete, last-minute travel to London might be compromised.