Currency in Tibet is Chinese Yuan. Chinese Yuan are available in notes of 1, 2, 5,10,20,50 and 100. Few ATMS and money exchanger are only in Lhasa. Bank of China provides facilities of exchanging foreign currency. It is hard to get change your currency out of Lhasa, so suggest you to get enough Yuan if you are planning tour out of Lhasa.
Credit cards are use only in big hotels of Lhasa and Shigatse. Beside that there are few shops accept credit card in Lhasa. Out of Lhasa and Shigatse, it is necessary to take Yuan cash everywhere. You tour cost for agencies can transfer by bank or provide cash at your arrival.