It is our first time to travel in the Western Europe part countries I did countless days of researching about their cultures, food, currency, etc.. I don't really like following about politics and economy that much, so my knowledge about it is only limited. My husband on the other hand, is an avid follower. I always count on him with regards to that subjects.
Prior our flight en route to Paris we change our US dollars cash-on-hand currency to Euro currency at Travelex inside the airport. They didn't charged us for a service fee since the cash we change is over 1thousand US$, if when we comes back from Europe and have remaining euro currency, they allow us to change it to US currency without again fees.
As a traveler it is very convenient to carry one currency to any European Union countries we go to. That way, we don't have to worry about exchanging currency every time we go to our next destination in Europe. Hustle free, indeed!
So yes, we use the same euro currency when we are in France and Italy.