Because of their northerly location, German wines are at the whim of the weather gods - too little exposure to the sun and the grapes do not have the depth to grow to their full potential.  As a result of this, the Germans created a system of classification that puts "where the grapes come from" secondary in importance to "what the ripeness of the grapes are."  The following classifications start at the lowest level of quality:

Literally translated as table wine, Tafelwein is the lowest classification of German wine.  In general, it is consumed locally.  It is important to note that the label must read Deutscher Tafelwein to actually be from Germany, not another European country.

The German version of the French Vins de Pays, Landwein is from a specific Landwein region and tends to have more body and character than the Tafelwein, as it must be riper at harvest.

This is the lower of the quality wine categories and is where most German wines are classified.  With the name literally meaning "quality wine from a defined region," these wines must come from one of the 13 specified wine-growing regions (e.g. Mosel-Saar-Ruwer) and contain only approved grape varieties that have ripened to a certain level and display the style and taste of that region.  These wines are meant to be consumed while still young.

Literally meaning "quality wines with special distinction or attributes," this is the category that includes all the finest wines of Germany and is what most American consumers are accustomed to.  The biggest difference between QbA wines and QmP wines is the QmP wines are made from grapes that are sweet enough to not need additional sugar.  Each wine is categorized into one of the following:

The lightest of the QMP wines, Kabinett wines are made with fully ripened grapes.  Because of their body, they make excellent quaffing wines or aperitifs. 

Literally meaning "late-harvest, Spätlese is made from grapes picked after the general harvest is over.  More intense in their flavor, these wines aren't necessarily always made into sweet wines.  In fact, they are being made dry (or trocken) more and more frequently.  Good with richer foods, they can also be enjoyed by themselves.

These wines are made from selected bunches of grapes that are picked one week after the rest of the harvest (sometimes using grapes with noble rot).  They are usually luscious, sweet wines, but are more and more frequently being made in a dry style.  In a good vintage, an Auslese can be sold at cheaper prices than the riper Beerenauslese.

The grapes that go into these wines are individually selected and are overripe.  The resulting Beerenauslese is a remarkably rich, sweet dessert wine.  Frequently, there are vintages where no Beerenauslese is produced in all of Germany.

The grapes for these wines are left on the vine so long that they become shriveled, resulting in a sweet juice that is incredible rich, sweet, luscious, and honey-like.  Due to the rarity of this wine being produced, they tend to demand extremely high prices.

These dessert gems are made from grapes that have Trockenbeernauslese ripeness, but have been left on the vine into December, when the weather conditions drop below 18º F (-7º C) and the grapes freeze solid on the vine.  At this point, they are harvested pressed, with the water crystals remaining in the press due to the freezing point of the juice being lower than the water. The result is a remarkably intense and balanced wine that is extremely high in sugar and acid, which makes them very easy to drink and refreshing.  These wines can be drunk while young, but also have great aging potential.