Code 39 (also known as USS 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 the model number etc. It is designed to encode 26 upper case letters, 10 digits and 7 special characters:

A, B, C, D, E, F, G, 
H, I, J, K, L, M, N, O, P, Q, 
R, S, T, U, V, W, X, Y, Z
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
-, ., *, $, /, +, %, SPACE.

Each code 39 symbol begins with a start character and ends with a stop character. Traditionally the start/stop characters are represented by asterisk character (*). Due to this reason, some applications include asterisks in the human readable text. The asterisks are not part of the encoded message and should not appear within the message.

Code 39 allows an optional checksum digit based on modulo 43 algorithm. The health industry has adopted the use of the check character for health applications and these types of barcodes are often referred as HIBC.

Property Code39OptionalCheckDigit specifies whether an additional check digit should be added to the barcode. Another property, Code39StartStopChars, when it is set to TRUE, adds the traditional start/stop characters (*) to the beginning and the end of the human readable text.