Pumpernickel is a type of sourdough bread from Germany that is made with a combination of rye flour and rye meal (more coarsely ground than flour) and is very dark in color (even when compared to breads made with flour that includes bran). It tastes very similar to rye bread, but differs in that pumpernickel recipes often call for molasses, helping to give pumpernickel its dark color. Pumpernickel is extremely dense; a pound of it has a volume equal to that of about 1/3 pound of wheat bread.

Traditional German pumpernickel contains no coloring agents (such as molasses), instead relying on the Maillard reaction to produce the characteristic deep brown color, sweet dark chocolate coffee flavor, and earthy aroma. Loaves produced in this manner require 16 to 24 hours of baking in a low temperature (about 250 degrees Fahrenheit) steam-filled oven. They tend to have a much more intense flavor than the approximations provided by adding molasses, coffee, cocoa powder, or other darkening agents employed by many bakeries. Other than in a few traditional German bakeries, most bakers eschew the long baking time for obvious economic reasons and, in addition to coloring and flavor agents, often add wheat flour (to provide gluten structure and increase rising) and commercial yeast (to quicken the rise compared to a traditional sourdough). The result is a loaf that resembles commercial rye bread with darker coloring. Many bakers also add a significant amount of caraway seeds, providing an alternate flavor that is now characteristic of many commercial pumpernickel (and light rye) breads.

The word "pumpernickel" derives from the Old High German words "pumpern", to fart, and "Nickel", a demon or goblin. The bread got this name for its supposed indigestible quality, although modern pumpernickel breads seem to lack this feature. There is an alternate popular etymology that Napoleon said that pumpernickel bread was only fit to be fed to his horse, Nicole -- that it was "pain pour Nicole". However, dictionaries do not support this etymology.

Pumpernickel is a relatively unpopular type of bread and is often difficult to find at supermarkets and smaller groceries.

Pumpernickel loaves are almost always baked without a baking pan, resulting in a rounded loaf.