For a spirit to be considered gin, it has to have at its most elementary level, a distinct juniper component. Beyond that, gin is not closely regulated; it's made just about everywhere in a slew of different styles that vary widely depending on the botanicals (besides juniper) used in distillation, as well as the amount of sugar added, and the resulting texture.
LONDON DRY GIN The white-button-down classic that's been around since England lost its mind for gin in the nineteenth century. A London dry is clean, dry, juniper-forward, and Martini-ready.
SLOE GIN This reddish purple spirit isn't so much a gin as a liqueur made from infusing gin with the tart-sweet juice from sloe plums. Best known for its presence in the Sloe Gin Fizz, sloe gin can be used in place of any fruit liqueur, especially in cobblers or Champagne cocktails.
AMERICAN The American craft spirit movement has produced a host of idiosyncratic gins that range from citrusy to peppery to floral. "Navy-strength" gins high-proof gins clocking in around 60% ABV have also become popular of late.
PLYMOUTH GIN Plymouth is defined by its place of origin: Plymouth, England. The style is very similar to a London dry (and can be used interchangeably), but it's fuller bodied with a more earthy botanical mix. Use this when you want to add textural complexity to a gin drink.
OLD TOM GIN Slightly sweet, with a touch of malt flavor, this pre-Prohibition style bridges the gap between genever and a London dry gin. It's become the go-to among bartenders looking to re-create the classic drinks of that era, especially the Martinez.
GENEVER Long considered the predecessor to gin, genever originated in Holland in the sixteenth century. It's built from a malted-grain base and has a less prominent botanical component than the crisp, aromatic gin we know today.