Ingredients: gin, dry (white) vermouth.
Fill a cup with ice and pour in a large jigger of gin and one-fourth to one-eighth as much vermouth. Strain into a chilled cocktail glass which contains a pitted (possibly stuffed), green olive or a twist of lemon peel (rub the rim of the glass with the peel and then drop it in).
Technically, this is a Dry Martini; the "standard," sweeter martini uses a ratio of two to one, but in fact no one ever makes them this way. With red vermouth instead of white and a ratio of two to one, this is called a Sweet Martini although "sweet" is also used to mean "with more vermouth" (in other words, "sweet," not "wet," is the opposite of "dry"); with a cocktail onion as garnish this is a Gibson; with vodka instead of gin this is a Vodka Martini; with vodka but garnished with a black olive this is a Buckeye; The James Bond of literature apparently drank vodka martinis made with Lillet. I had a great martini at Lola's in Los Angeles with Pernod replacing the vermouth. Some add bitters; I don't like it with angostura bitters, haven't tried lemon bitters.
This is the truly personal cocktail in both ratio and garnish. I slightly prefer a twist of lemon peel for the flavour it adds to the drink, but I love to eat the olive; I sometimes do both at once. The Joy of Cooking reccomends a fresh hazelnut, which is good. The cocktail glasses must be cold - either put them into the fridge well in advance or sit some ice in the glasses for a few minutes before starting. In a taste test performed with some friends, we decided that Bombay Sapphire makes the best martini and my own research recommends Noilly Pratt vermouth. I have not detected a taste difference between shaken and stirred, but if a large number are being made in one batch, shaking is necessary to get the gin cold quickly. Martinis made with gin kept in the freezer are stronger than those begun at room temperature because the latter contain more melted ice. Vermouth lives longer if kept in the fridge; throw it out if it gets a dusty or dirty taste.