The unit of Turkish money is the Turkish Lira (Türk Lirası, TL or TRY). A unique symbol was introduced by the Turkish Central Bank to denote the Turkish Lira.
Banknotes are in denominations of TL1 (rare), 5, 10, 20, 50, 100 and 200 (rare) liras.
The lira is divided into 100 Kuruş (koo-ROOSH), with coins in denominations of Kr 1 (rare), 5, 10, 25 and 50 (Kuruş). Read more about the history of the Turkish lira.
Where to Obtain Liras
It's usually best to obtain your Turkish liras in Turkey rather than before you leave home, as the exchange rates outside Turkey are usually not as good as those inside the country.
The easiest way to get cash liras is to stick your home bank card or credit card into a Turkish ATM (bancomat/cashpoint, cash machine).
You can exchange foreign-currency cash at a Currency Exchange Office (Döviz Bürosu). Note that exchange rates at international airports in Turkey are usually worse than rates in city centers. In Istanbul or touristic areas, it’s easy to find places to exchange your money, but you may need to provide your passport and other details.
Credit Cards, Travelers Checks
Credit and debit cards are widely used in Turkey, but there are special situations you must know about.
Travelers Checks are a bother, and not recommended.
When to Use Cash Liras
Although some large travel expenses such as hotel rooms and car rentals may listed in US dollars or euros, they may also be paid in Turkish liras. Some establishments offer discounts for payment in cash (because then they need not pay a percentage to the credit card company).
When paying with foreign currencies, Euros are most readily accepted, US dollars are good, UK pounds sterling are accepted in some places, but no Scottish notes! Other currencies should be exchanged at currency exchange offices.
Carrying Cash
Should you carry a lot of cash? That's up to you. Except for pickpockets, Turkey is a relatively safe country, but nowhere is completely safe. I would say the chance of loss is remote if you carry your stash underneath your clothing in a waist belt, neck pouch, etc. Most hotel rooms of 3 stars or more have small private safes in their guest rooms for valuables.
Small Notes, Big Notes
Many people in Turkey will not accept large bills/notes for small payments, so it's good to juggle your TL cash-on-hand so that you always have some smaller amounts. Get in the habit of paying with bills/notes that are about equal to twice the amount you're paying (so pay for a 48TL meal with a 100TL note, which gives you 52TL in change). Not every establishment or taxi company accepts payments by card or keeps large amounts of change on hand. If you give notes that are three times or more than the price, you're likely to be asked for smaller notes or the cashier might go to a shop next door to try and get change. It’s better to avoid the awkwardness of this situation altogether by keeping smaller notes with you.
Leftover Liras
LeftoverCurrency.com says it will buy these old notes from you.