When to arrive at the airport

It is just like in the USA; get to the airport two hours before departure to checkin and go through security where the lines could be long depending on the time of day.

With online checkin it is the security lines that take the longest anywhere in the world.

You should read the small print for each flight - each airline will tell you how many hours you should prepare to arrive at the airport. Those guidelines are probably a bit conservative, but at least they ensure you won't miss your flight. No one can predict how busy any airport will be at any given time. I've been really surprised to find long lines at even a small airport just due to bad timing.

I fly a lot within the US and never arrive that early lol I guess I don't fly out of major large cities either (unless Dulles counts)
I also don't want to risk missing a flight. I'll check to see if the arrival time is suggested for each flight. I'm also looking into global TSA pre check which might also help out.
Thanks!

TSA precheck and Global Entry both are just for air travel within the USA and when entering the USA respectively.
It does not apply to air travel in Europe

You are correct. I looked into it and TSA global only helps upon reentering into the US

European airlines generally require that you have completed your check-in and have a boarding pass in your hands at least 45 min prior to departure for an intra-Europe flight.
45 min is enough to go through security and walk to the gate at most European airports. I generally get at the airport about 75-90 min prior to be safe (or 1 hour if it's a small airport like Florence).

How risk-averse are you? Are you flying the airline's last flight of the day, or the first out in the AM? If you miss the last flight because you didn't give yourself enough time, where does that put you? Are you willing to roll the dice? I agree with the others that it can be a crap shoot regarding the amount of time that it takes to get through security. I always give myself two hours, and sometimes I will just make the plane here in Seattle (and that is with TSA PreCheck). Some airports are physically quite large, and it can take some time to walk to your gate. RS indicates that CDG is one of the large ones and that you should factor in an hour to get from one terminal to another. He also recommends arriving at CDG two hours before your flight (within Europe). Follow his, the airline's, and the airport's advice; if they all say two hours, why would you want to chance it?

There is no such thing as TSA Global. There is TSA Pre-Check and Global Entry.

TSA Precheck allows you to access certain security lines upon departing most U.S. airports when flying participating airlines. It is not just for travel within the U.S. It does apply to travel to Europe if the airline you are flying is a participating airline.

Global Entry allows you to use special computer kiosks when arriving into the U.S or utilizing a pre-clearance airport.

If you get Global Entry, you also get TSA Precheck. But not vice-versa.

The Global in Global Entry does not mean it can be used around the Globe.

Hi,

At Heathrow the electronic board tells you when you can start standing in line based on the time of departure indicated on your ticket.

At Heathrow the electronic board tells you when you can start standing in line based on the time of departure indicated on your ticket.

I have never seen this. I go through security when I get there. No one has ever stopped me.

Do you remember which terminal? I've flown out of 2,3 and 5 and never encountered it.

Why are you flying Paris to London?

The train (Eurostar) would be much easier and take less time.

Plane from Paris to London is already booked...but I chose it because it was WAY cheaper than the train and travel time was faster. (train 2 hrs 50 min vs plane 1 hr 15 minutes) Even though I know it will end up about the same after early arrival and all that. Still...money talks and I'm cheap lol
We aren't having any luggage so I don't have to worry about baggage fees. (just make sure everything is stuffed into one backpack)

Flying out of London, out of Croatia and out of Paris, you will also have to go through passport control. In Rome last week, I waited in line for 20 minutes for passport control on exiting the country, FWIW.

There is no passport control exiting London.

If you're flying Ryanair, there's a separate document check line you have to wait in; allow time for this.

Paris, London, and Rome all have more than one airport. (London has six - at least as far as the airlines are concerned). Be sure you go to the right one. Some of them are much larger than others, but I wouldn't count on any of them being uncrowded - or count on a fast time through security. As someone said above, how lucky do you feel?

Do heed MrsEB's point about luggage size. If you're flying a budget airline (Ryanair, Easyjet, Vueling, etc), these tend to enforce their rules strictly, as that's how they make their money. If your bag doesn't fit into the sizer, they will make you check it - and charge a higher fee for this at the airport than you would have paid in advance online. Get a tape measure, and measure your bag against the size restrictions for each flight you're taking (the airline's websites have the maximum bag sizes for each flight). Since each airline has different rules, and may have different rules for different routes, it is very possible that you will have to check your bag on at least one flight - even it's fine as a carry on for others.