It is served chilled, often by ice in a specific shaker, then drained into the signature-style glass.
The ratio of the two liquids is 5:1 (traditionally, 2 and one half ounces of gin to half an ounce of vermouth) usually, though by changing this, a person can make the drink "drier" (more gin) or "wetter" (less gin) depending on his tastes.
Martinis can also be made with other alcoholic bases, the most common alternative to gin being vodka (often called a Vodka Martini, Vodkatini, or Kangaroo)
Other variations of the Martini centre around the inclusion of other alcohol or flavours in the drink.
Steve: Nah, that stuff sucks balls. Let's get some Martinis down at the bar.