All foreigners, except for the nationals of Gulf Cooperation Council (GCC), require a passport and visa to enter Lebanon. The GCC nationals are issued three-month visas upon arrival in Beirut international airport. Visas can be obtained at any Lebanese embassy or consulate and are valid for six months for a stay of two months. 
If you have an Israeli stamp on your passport, you will be refused entry in Lebanon. Keep your passport with you at all times when travelling around Lebanon, as there are Lebanese and Syrian checkpoints all over the country. Being caught without your passport may create problems for you. Get your International Driving Permit (IDP) if you plan to drive in Lebanon. Also get your third party insurance even though it is not mandatory.