Code 39 is a barcode symbology that can encode uppercase letters (A through Z), digits (0 through 9) and a handful of special characters like the $ symbol. The barcode itself does not contain a check digit (in contrast to Code 128, for example), but it can be considered self-checking on the grounds that a single erroneously-interpreted bar cannot generate another valid character.

A serious drawback of Code 39 is its low data density; it requires more space to encode data in Code 39 than Code 128. This means that very small items can't be labeled with a Code 39-based barcode. However, Code 39 is still widely used and can be decoded by virtually any barcode scanner/reader.

One advantage of Code 39 is that since there is no need to generate a check digit; it can be integrated easily into an existing printing system by adding a barcode font to the system or printer, then printing the raw data in that font.