http://en.wikipedia.org/wiki/Champagne_%28wine %29
Champagne is a single Appellation d'Origine Contr�l�e. Grapes must be the white Chardonnay, or the red Pinot Noir or Pinot Meunier (a few very rare other grapes that were historically important are allowed, but very unusual). Champagnes made exclusively from Chardonnay are known as blanc de blancs, and those exclusively from the red grapes as blanc de noirs.
Champagne is typically light in color even if it is produced with red grapes, because the juice is extracted from the grapes using a gentle process that minimizes the amount of time the juice spends in contact with the skins, which is what gives red wine its colour. Ros� wines are also produced, either by permitting the juice to spend more time with the skins to impart a pink color to the wine, or by adding a small amount of red wine during blending. The amount of sugar (dosage) added after the second fermentation and ageing also varies, from brut z�ro or brut natural, where none is added, through brut, extra-dry, sec, demi-sec and doux. The most common is brut, although throughout the 19th century and into the early 20th century Champagne was generally much sweeter than what we see today.
Most Champagne is non-vintage, produced from a blend of years (the exact blend is only mentioned on the label by a few growers), while that produced from a single vintage is labelled with the year and Mill�sim�.
Many Champagnes are produced from bought-in grapes by well known brands such as Veuve Clicquot or Mumm.