The lekë is the official currency, though the euro is widely accepted; you'll get a better rate in general if you use lekë.
Accommodation is generally quoted in euros but can be paid in either currency. ATMs (found in most of Albania's towns, bar remote villages) usually offer to dispense cash in either currency.
Albanian banknotes come in denominations of 100, 200, 500, 1000, 2000 and 5000 lekë. There are five, 10, 20, 50 and 100 lekë coins.
Albanian lekë can't be exchanged outside the country, so exchange them or spend them before you leave.
Credit cards are accepted only in the larger hotels, shops and travel agencies, and few of these are outside Tirana.
It's polite to leave your change as a tip.