Until the construction of the "New Uffizi" (but certainly not because of it - this situation has been in place for awhile!) is complete, the following outlines how to enter the Uffizi - if you have a ticket reserved, if you need to buy your tickets, if you are a "Friend of The Uffizi", if you purchased the Firenze Card, etc.
There are 3 doors you need to know about, and they are all on the Piazza degli Uffizi. See the image/map to the right for the layout. They are described in more detail below.
Door Number 1 is the entrance if you already have a reservation and have picked up your ticket, or are part of a group, tour, school trip, etc. If you are facing the building the left side of the entrance is for groups, and the right side is for individuals, families, etc. This is also the entrance you want to use if you have the Firenze Card in your possession (which means you usually beat any lines also). You should show up here 10 minutes before your timed reservation (who knows why in a country where being late is a perpetual state). You do not need a time with the Firenze Card, but you may have to wait a little bit to enter - I wouldn't think more than 10 minutes or so (this may not be the case in high season, but still any wait here will be shorter than the general admission line).
Door Number 2 is the main entrance, and also the place where the line starts if you are buying a ticket for that day. The line goes down the arcade toward the Arno. It can be quite a wait. If you ever plan to visit without a reservation or a Firenze Card or Friends of the Uffizi card etc., the best advice is to go later in the day. For most of the year, from Spring until mid-November, there is a line here of some length (in the summer it is hours long), but it is ALWAYS longer in the AM, especially on weekends.
At this same door you will usually see the ropes aligned that allow a small space to enter on the left hand side - this is the office for the Friends of The Uffizi where you can buy the card. Note however that even if some signs say you enter at door number 1 with the Friends of The Uffizi card, I have always had to enter at door number 2 (the guard will allow you to cut the line when you show him your card) and then get a "Free" ticket by showing the card and ID. This is serious - make sure you have picture ID if you plan on using the Friends of The Uffizi card, for adults and children. I had a nasty (and I must say the only one I ever had in Florence) tourism experience here once when someone in the ticket booth seemed to think I was taking the ID request for my children too lightly, which I wasn't. I just had entered with them several times prior and was never asked for their IDs, so when I was and didn't respond formally I was treated rather rudely.
Door Number 3, which is across the Piazza degli Uffizi on the west side or wing, is where you may pick up your tickets if you have made a prior reservation. They ask you only do this 10 minutes before your reserved entrance time, I guess to try to keep the line down. Another thing to note - there are many, many ways to reserve a timed entrance ticket to the Uffizi - and some of them are just that - reservations (which you pay extra for) and not the ticket itself. So make sure you are prepared depending on who or what service you used. You may have to pay additionally for the ticket if all you paid for upfront was the reservation. Not sure why but I know some tourists that can not get their heads around this fact!
So that is basically it. Things can change, and there are always various paper notes taped to any of these signs on any day, but usually the staff outside of doors 1 and 2 (who usually are not in uniform but have ID around their neck) are very helpful and speak English if you get confused.
The official site for tickets and reservations, sanctioned by the Uffizi, is b-ticket. There have been various reports on other websites of the b-ticket site not working with certain credit cards, etc. but also many more that say it does. You can also call their phone number if you need to. Remember the museum is closed on Mondays all year round.
For guided tours of the Uffizi we suggest browsing the many options on Viator from our sister site Florence Journal - there are several variations and price options.
Please remember that this advice is given for informational purposed only and is subject to change at any time!