Code 39, also known as Alpha 39, Code 3 of 9, Code 3/9, Type 39, USS Code 39, or USD-3, is a common barcode type used for various labels such as name badges, inventory and industrial applications. It's also the standard for many government barcode specifications, including the U.S. Department of Defense. Being the first alpha-numeric symbology to be developed, it is still widely used-especially in non-retail environments.

The symbology of the Code 39 character set consists of the digits 0-9, the letters A-Z, and the following symbols: space, minus (-), plus (+), period (.), dollar sign ($), slash (/), and percent sign (%). The Code 39 uses an asterisk character as a start/stop character which should not be part of the data in the barcode.

Each character including 3 wide and 6 narrow elements consists of 9 elements: 5 bars and 4 spaces. Characters are separated by an inter-character gap which is the multiple width of a narrow bar. The length ratio of wide element and narrow element may be in the range of 2.0:1 to 3.0:1.

The following chart defines all the Code 39 character assignments:

NOTE 1 S/S means the start and stop character, usually graphically represented as *

NOTE 2 In the columns headed B and S, 0 stands for a narrow element and 1 represents a wide element