Bourbon is an American whiskey, a type of distilled spirit, made primarily from corn (maize) and named for Bourbon County, Kentucky. It has been produced since the 18th century. While it may be made anywhere in the United States, it is strongly associated with the Commonwealth of Kentucky.
On May 4, 1964, the United States Congress recognized Bourbon Whiskey as a "distinctive product of the United States." The Federal Standards of Identity for Distilled Spirits (27 C.F.R. 5.22) state that bourbon must meet these requirements:
Bourbon must be made of a grain mixture that is at least 51% corn.
Bourbon must be distilled to no more than 160 (U.S.) proof (80% alcohol by volume).
Neither coloring nor flavoring may be added.
Bourbon must be aged in new, charred oak barrels. 
Bourbon must be entered into the barrel at no more than 125 proof (62.5% alcohol by volume).
Bourbon, like other whiskeys, may not be bottled at less than 80 proof (40% alcohol by volume.)
Bourbon which meets the above requirements and has been aged for a minimum of two years, may (but is not required to) be called Straight Bourbon.
Straight Bourbon aged for a period less than four years must be labeled with the duration of its aging.
If an age is stated on the label, it must be the age of the youngest whiskey in the bottle.
Only whiskey produced in the United States can be called bourbon.
Bourbon bottle, 19th century.
In practice, almost all bourbons marketed today are made from more than two-thirds corn, have been aged at least four years, and do qualify as "straight bourbon"—with or without the "straight bourbon" label. The exceptions are inexpensive commodity brands of bourbon aged only three years and pre-mixed cocktails made with straight bourbon aged the minimum two years. However, a few small distilleries market bourbons aged for as little as three months.
National Bourbon Heritage Month
On August 2, 2007, the U.S. Senate passed a resolution sponsored by Senator Jim Bunning (R-KY) officially declaring September 2007 "National Bourbon Heritage Month", marking the history of bourbon whiskey. Notably, the resolution claims that Congress declared bourbon to be "America's Native Spirit" in its 1964 resolution. The 1964 resolution, however, does not contain such a statement per se; it only declares that bourbon is a distinctive product identifiable with the United States in the same way that Scotch is identifiable with Scotland. The resolution has been passed each year since.
Bourbon may be produced anywhere in the United States where it is legal to distill spirits. Currently most brands are produced in Kentucky, where bourbon has a strong association. Estimates are that 95% of the world's bourbon is distilled and aged in Kentucky. Bourbon has also been made in Colorado, Kansas, Illinois, Indiana, Missouri, New Jersey, New York, Ohio, Pennsylvania, Tennessee, Texas, and Virginia.
Bardstown, Kentucky, is called the Bourbon Capital of the World and is home to the annual Bourbon Festival in September.
The Kentucky Bourbon Trail is the name of a tourism promotion intended to attract visitors to six well-known distilleries: Four Roses (Lawrenceburg), Heaven Hill (Bardstown), Jim Beam (Clermont), Maker's Mark (Loretto), Wild Turkey (Lawrenceburg), and Woodford Reserve (Versailles)