Green Onion
Also known as scallions or spring onions, green onions are the immature shoots of the bulb onion, with a narrow white base that has not yet begun to swell and long, flat green leaves. Recipes often specify whether to use only the white base, the green tops or both. Green onions have a mild flavor and can be enjoyed raw in salads, while their chopped or minced green tops are often used as a garnish. Whole green onions can also be grilled or braised like leeks. The white base may be substituted for shallots.

Maui, Vidalia and Walla Walla Onions
These fresh onions are mild, sweet and juicy and named for their place of origin since, due to soil and climate, they lose their sweetness if grown elsewhere. Maui and Vidalia onions, from Hawaii and Georgia respectively, come into season during spring, and Walla Walla, from Washington, during late summer. These onions are best eaten raw in sandwiches or salads.

Pearl and Boiling Onions
Pearl onions are small dried onions no more than 1 inch in diameter and are available in red or white. Boiling onions are white and slightly larger. Both have a mild flavor similar to that of green onions. They are often served as a garnish for stews, roasted meats and marinated salads, or used for braised or creamed onions.

Red Onion
Also called Italian onion and Bermuda onion, this purplish red onion is mild and slightly sweet. It is delicious raw in salads, sandwiches and relishes and briefly cooked in vegetable mixes. Sweet elongated varieties, found in farmers' markets, are called torpedo onions.

This small member of the onion family looks like a large clove of garlic covered with papery bronze or reddish skin. Shallots have white flesh lightly streaked with purple, a crisp texture and a flavor that is subtler than that of an onion. They are often used for flavoring sauces and salad dressings that would be overpowered by the stronger taste of onion.

Spanish Onion
This very large, round yellow onion is similar to yellow onions and used in the same way.

White Onion
More pungent than the red onion but milder and less sweet than the yellow, the white onion is a favorite in Mexican cooking. Large, slightly flattened, mild white onions are sometimes called white Spanish onions.

Yellow Onion
The yellow globe onion is the common, all-purpose onion sold in supermarkets. It can be globular, flattened or slightly elongated and, since it is dried, has a parchmentlike golden brown skin. It usually is too harsh for serving raw but becomes rich and sweet when cooked, making it the ideal onion for caramelizing.

Adapted from Williams-Sonoma Kitchen Companion (Time-Life Books, 2000).