Green tea is tea that has not been oxidized. Black and oolong teas, by contrast, are allowed to oxidize (Black teas fully, oolongs partially), thus turning the leaf a darker color, and changing the chemical composition, flavor, and aroma of the leaf and brewed cup. Green tea comes in many different varieties and is produced in many different regions.
Japanese Green Teas:
Sencha is the most well-known Japanese green tea, popular both in Japan and in the rest of the world. Sencha is produced by first steaming the leaves and then pan-firing them. Sencha can have a sharp flavor; its aroma is often described as being reminiscent of seaweed. Although sencha originated in Japan and is most commonly produced there, it is also produced in a number of other countries, including China, Vietnam, and even (rarely) Sri Lanka.
Japan also produces a myriad of unique varieties of green tea, many of which are unlike anything else available. Matcha, a powder made by grinding up the whole tea plant, produces a bright green opaque cup, and is also used to flavor ice cream, cakes, or pastries. Bancha is a basic everyday drink, usually less expensive than sencha. Hojicha is made by roasting the tea leaves. Genmaicha is made by mixing tea (usually sencha or bancha) with toasted rice and sometimes popcorn, and often with matcha as well. Kukicha is made of twigs and stems of the tea plant. Lastly, gyokuro is produced by shading the leaves during the last weeks of production. Hojicha and kukicha tend to be lower in caffeine, although both still contain some caffeine.
Chinese Green Teas:
Gunpowder is a Chinese tea with tightly curled leaves and a strong smokey aroma. Young hyson is similar to gunpowder, but slightly less smokey. Chun mee is a particular grade of young hyson. These teas are all pan-fired (not steamed) teas and tend to be relatively inexpensive and have a relatively sour taste.
Dragon well, also known as lung ching, is a lighter pan-fired tea that tends to have a more delicate flavor, and can be quite expensive. Other well-known Chinese green teas include bi luo chun (meaning green snail spring), a tightly-curled tea made from leaves gathered in spring, and lu an melon seed, a tea made exclusively from the second leaf on each branch.
Green Teas from Other Regions:
Thailand, Vietnam, Indonesia, Laos, and Korea all produce green teas as well, each with their unique qualities. These countries, in addition to producing their own unique varieties of tea, also make teas (such as sencha, young hyson, gunpowder, or dragon well) in the style of well-known Chinese or Japanese varieties; even if produced in a similar manner, these teas have a unique character, owing to the differing climates between these regions.
Darjeeling, a district in India best known for black teas, has also begun to produce more green teas in recent years. A similar trend is happening, although more slowly and to a smaller degree, in other regions, including Assam, India, and also Sri Lanka (Ceylon), and Kenya.