Code 39 is also known as Code 3 of 9.

Code 39 is the most popular symbology and is what we recommend to the first-time user.

Code 39 Full ASCII - Standard Code 39 contains only 43 characters (0-9, A-Z, $, /, %, +). Code 39 Full ASCII can be extended to an 128 character symbology (full ASCII) by combining one of the special characters ($, /, %, +) with a letter (A-Z) to form the characters that are not present in the standard Code 39 symbology. For example, in standard Code 39 a lowercase "a" cannot be represented. In Code 39 Full ASCII, a lowercase "a" is represented as "+A". 

Code 39 Standard - is variable length and is the most frequently used symbology in industrial barcode systems today. The principal feature is to encode messages using the full alphanumeric character set. Three of the nine elements (bars) are wide and six elements are narrow. The Code 39 barcode uses four special characters "$", "/", "+", "%" which can be paired with alphanumeric characters to extend to the full ASCII character set.