Cuban Departure Tax
A Departure Tax of 25 CUC (equivalent to $25 USD) must be paid by every travellers when leaving Cuba. Are exempt: Diplomats based and accredited in Cuba, Children under 2 years, transit passengers (arriving and departing within the same day, no overnight stay allowed, and not leaving the transit area), government employees travelling on duty, crew members travelling on duty.
This tax is payable in CASH ONLY, and in no other currency than CUC (Cuban Convertible Pesos).
In every Cuban airport there are one or more --Departure Tax-- windows near the check-in counters. This is where you must go to pay the tax AFTER you've checked-in with your airline. A hologram sticker will be affixed to the back of your boarding pass as proof of payment. Here's a picture of this stamp:
Cuban Departure Tax Stamp (real size: approximately 1½ X 1 inch)