Code 39 (also known as USS ^[4] Code 39, Code 3 of 9) is the first alpha-numeric symbology developed to be used in non-retail environment. It is widely used to code alphanumeric information, such as model numbers etc. It is designed to encode 26 upper case letters A-Z, 10 digits 0-9 and 7 special characters - hyphen (-), period (.), dollar sign ($), forward slash (/), plus sign (+), percent (%) as well as the space character.

Code 39 can have an optional modulo 43 check digit. It also has a variant called code 39 extended or code 39 full ASCII, which is capable of encoding all 128 7-bit characters (ASCII values 0 - 127).

Code39 is a fairly simple symbology. Still, you can not just type the number and format with the font. A code39 barcode string includes additional characters, such as start/stop characters and checksum character. Due to limitations imposed by the font technology, you need to enter another character for space. We'll go through these topics one by one below.