Different types of onions include scallions, yellow onions, Spanish onions, Vidalia onions, red onions, shallots, pearl onions, leeks and cipollinis. Scallions are also called green onions; they have a delicate flavor and can be eaten raw or added to dishes at the last minute. Both the white part and the green part can be eaten. Because they are full of water, they don't have a long shelf life.
Leeks are long onions that have a more delicate flavor than regular onions. They look like scallions, with a white bottom and a green top, but are much larger and more robust. They can be stewed or braised and added to vinaigrette. Because much of the plant grows underground, cleaning leeks can be time-consuming.
Cipollini onions are white and flat and have a sweeter taste than regular onions. Like scallions, they have a lot of water and should be used as soon as possible.
Red onions have less sugar than yellow and white onions and don't caramelize as well. However, they are excellent if eaten raw in salads.
Shallots are small onions that are often found in delicate sauces and preparations. They have a papery texture like yellow onions, but their flesh is often tinged with purple.