Greetings vary quite a bit depending on the culture, and if you're travelling, you don't want to be caught off guard. The New York Times has a useful guide to common greetings in different countries.
Photo by Tim Gouw
If you're visiting the US, you're probably safe to go with a simple handshake or a hug, but in a lot of cultures, kissing is the go-to greeting. How to kiss varies depending on the country, too, though. They explain:
In much of Latin America, Europe and the Middle East, air kissing between strangers is common, but each nation, and in some cases each region within a country, may have its own habits.
Argentine men will cheek-kiss one another, but only if they are friends of friends. In most of the Arab world, a double air kiss is obligatory, though only between people of the same sex. <br< ...In Portugal, the kissing usually progresses from left to right, but in Strasbourg, France, it's right to left.
In Japan, a simple bow will do, and as the article explains, most of north Europe greets with either a handshake or a single kiss for friends. It's a quick, useful guide for travellers, and you can check it out at the link below.
A Traveller's Guide to Customs: When to Shake Hands, Hug or Kiss [The New York Times]