The kiss or the handshake?

As you may or may not remember, my husband MBM works with people from all over the world. Mexico, Argentina, Columbia, Switzerland, France, Germany, South Africa, etc.

Today, we had about 15 of his co-workers over. Several Americans (though not all from Kentucky) and several from Switzerland and France.

Here's the question: do you shake hands or do the cheek-to-cheek kiss? I didn't do so well this time. But I think I'm going to need to know this for future work-related events.

If I have NEVER met the person before, what do I do? At the beginning? And then at the end?