How do I make an Americano?

The story goes that it was created in America by an Italian barista who was serving espresso-based coffees, but when a customer asked for a long black coffee, the barista improvised and created this drink. When asked what it was, he called it an Americano. It is typically served in a medium sized cup and is simply made by using a shot or two of espresso and topping it up with hot water.