Train from Paris to London

The UK isn't part of the Schengen Treaty, so you will have to show your passport at the Immigration checkpoint in both directions.

Terrific! Thanks! That means a new Stamp in my passport!

Make sure to arrive at the train station within the time allowance provided. You need the time to fill out the immigration forms and get processed. This occurs PRIOR to departure, not on arrival as it does with international flights. And FYI - anytime you cross an international border, you MUST have your passport. The Schengen nations may not ask for it and will not stamp it, but in some rare cases they do check and it is the only proof of identity/nationality.

You will go through immigration/passport control and security in Paris as part of the check-in process. When you get to London you can get off the train and be on your way. You will do the same in London for your return and when you get to Paris you can get off the train and be on your way. There is a mandatory 30-minute check-in deadline for the Eurostar. Lines can move slowly. I recommend that you be at the station one hour before your scheduled departure time.

We like to arrive early when taking the Eurostar between Paris and London, which we do at least annually. Both rail stations, St Pancras and Gare du Nord, are well equipped with places to grab a paper, a coffee and a pain du chocolat, or a sandwich and cold drink to take on the train, and it's always entertaining to people watch. The line for immigration check in can be quite long on popular days of travel so arriving maybe 2 hours or 90 minutes ahead of departure is always a good idea on weekends or Fridays and Mondays when the business travelers are in abundance. Relax and enjoy the delightful train ride.

Stephanie, By the time you come back and land at LAX (presumably), you should have five stamps in your passport, the last one being US Admitted.