There are two official currencies in Lebanon, which are bound to each other, the Lebanese Lira/Pound (LBP), and the US Dollar (USD). You can officially pay with either currency throughout the country. It might happen that after paying in once currency, change will be given in form of the other. Oftentimes, the currencies are even getting mixed. One USD currently amount to 1.5000 Lebanese Lira.
It is very easy to exchange money (Euros or US Dollars) anywhere in the country or to withdraw cash with a debit or credit card, as the banks have numerous branches. We recommend to take a part of the money in cash, and take a debit or credit card with you as well. Withdrawal fees might vary according to the regulations of your home bank.