Travel to Lebanon could not be easier these days. A growing number of airlines service Beirut, which has frequent connections to Europe, Africa, Asia and the rest of the Middle East. There are no direct flights to the USA. Flights between Beirut and Tehrãn resumed in 1999 after a 20-year absence caused by the Iranian revolution and the Lebanese civil war. Beirut airport is 5km (3mi) south of the city centre.
Syria is the only country that currently has an open land border with Lebanon - the border with Israel is likely to stay closed for some time. Lebanese visa rules change frequently, so check with your embassy for the latest rulings. Currently, you can obtain a visa when entering Lebanon from Syria at the border and vice-versa.
Buses run between Beirut and Damascus every hour from 06:00 to 20:00 and there are buses and service taxis from Beirut to Lattakia and Hama (as well as Aleppo and Homs). From Tripoli there are buses to Hama, Aleppo and Damascus (as well as Lattakia and Homs).
If you're planning to drive into Lebanon, be prepared to pay a hefty fee (in cash) at the border - though it's refundable when you leave.
Lebanon is a tiny country: you can drive from one end to the other in about three hours. Most people use service taxis to get around, a huge number of which run like buses on set routes; they carry around five passengers, each of whom chip in for a fifth of the fare. The other system, private taxis, is a more traditional approach with the taxis taking you where you want to go for a negotiated fare. There are also many 'pirate taxis' cruising for fares. These are more expensive than service taxis, but look very similar, so it's best to ask before you get in.
Bus networks are extensive, but some buses are poorly maintained, and also go too fast; accidents do happen. Generally, however, buses are reasonably safe, comfortable and reliable and are very cheap by Lebanese standards. It's unlikely that the country's rail service will be restored in the near future.
Car rentals are fairly expensive in Lebanon but if you shop around you can find surprisingly reasonable prices. The country is notorious for the bad condition of its roads and the hair-raising driving style of its drivers. Road rules are effectively nonexistent, traffic jams are ubiquitous and there are no speed limits. On the upside, in theory everybody has agreed to drive on the right and fuel is cheap and easy to obtain.