Immigration on layovers

Going off your itinerary, you'd be looking at:

Newark to Dublin - immigration/customs*
Dublin to Paris - immigration/customs*
Paris to Rome - no immigration/ no customs
Rome to London - immigration/ no customs
Edinburgh to Rome - immigration/ no customs
Rome to Newark - looonger immigration/customs ;)
*depending on flight bookings

Is the Newark (to Dublin, then on) to Paris a single booking? Or did you book two entirely separate flights? That's more relevant to customs than it is immigration, because that'll determine what your luggage is up to. If you booked two entirely separate flights, you'll likely need to retrieve your luggage and clear both customs and immigration in Dublin, then re-check the luggage for the flight on to Paris. If it's a single booking, you'll check your luggage in Newark and not see it until Paris (and clear customs there). Keep in mind customs and immigration are two distinct things - immigration is, in a nutshell, down to your passport and you as a person, customs about your luggage and whatever items you're traveling with.

Ireland isn't a Schengen area country, which means you'd not only go through immigration once arriving from the US and leaving the airport, but again once arriving in Paris from Dublin. Having said that, immigration is often simple enough once there and you're looking at mostly a customs-free zone throughout the EU.

Once in Paris and traveling on to Rome, you might as well be on a domestic flight as both France and Italy are Schengen area and don't require passport control to travel between them. Ireland and the UK are not Schengen. But that means, when traveling back to London from Rome, you're traveling back out of Schengen, then back in once heading back to Rome. You sure have quite the itinerary!

https://www.ricksteves.com/travel-tips/trip-planning/travel-documents
Has more info on Schengen (scroll down a lil ways).

Normally, if you were "passing through" you would not go through immigration in Dublin. But since you want to leave the Airport, then yes, you will go through immigration. On return to the Airport, you will go through security, and then likely some type of passport check.

On arrival in Paris...Immigration again (entering the Schengen zone)

Paris to Rome, only normal Security.

Rome to London, have to go through Immigration in London

Edinburgh to Rome, Immigration in Rome

Obviously immigration on return to US.

Perhpas a little note on terminology. Many people use the word "customs" to mean the entire immigraiton procedure when in fact immigration (passport control) and customs (for goods) are two separate things.

Much of Europe is in what is called the Schengen zone. No immigration between countries in this zone. France and Italy are part of this so there is no immigration between these two. However, Ireland and the UK are not. So you will go through immigration based on your itinerary when entering the two. As you will when returning to the USA. (The only time you won't go through immigration is Paris-Rome unless your retun to Rome prior to returning to the U.S. is just to change planes.)

As for customs, in almost all cases, you will just walk through either a green "door" or a "blue" door. There is no real door but the passageway is painted that color.

Since you are only doing carry on you don't have to worry about your bag being tagged.

The previous posters have answered your question spot on! By he how many weeks is your trip?

Did you already booked all the flights? A more simple logistical route for your trip could have been:

Newark to Dublin
Dublin to Edinburgh
Edinburgh to London
London to Paris - via train
Paris to Rome - via train
Rome to Newark

1885BD and Paul, thank you both so much!

Frank II - you're right, I goofed with my terms.

RJean - I have to go in a specific order for flights because the two Rome portions are part of a study abroad, which take up 2 months of my time. Otherwise I would have been a lot more logical with my plans, and taken more trains! But planes take less time and are in these cases less expensive and I don't want to spend the time I have on a train instead of exploring.

Ed - I will be traveling for 82 days (just avoiding the 90 days rule)!

Also remember that when you leave Rome both times, you will go through exit immigration. (You're passport will be stamped to show you left Schengen.) But that shouldn't take too long.

No exit immigration from Ireland or the UK.

Frank II, wait, so how many passport stamps will I end up with after all this? keeping in mind that I will be exiting Dublin airport and then coming back in?

• You get a stamp on entry for Ireland, but not on exit.
• You get stamps for entry (Paris) and exit from (Rome) the Schengen Area. But not when travelling within the Schengen Area (Paris to Rome).
• Stamp on entry to the UK (London), but not on exit (Edinburgh)
• Again on entry to and exit from the Schengen Area (Rome).

I count 6 stamps. Assuming your home country does not stamp you.

BTW, UK and Ireland rely on the airline informing the governments of passenger details including passports, so no passport checks on exit. Schengen Area checks on entry and exit. They have land borders airlines are not always involved.

For your London to Paris train, the French passport officer will check your passport at London St. Pancras station, before you get on the train. It will be stamped for French entry in London!