Code 128
This symbology is a very compact bar code for all alphanumeric applications. The full (128-character) ASCII character set can be encoded in this symbology. If the bar code has four or more consecutive numbers (0‹9), the numbers are encoded in double-density mode (where two characters are encoded into one character position). It has two forms of error checking, making it a very stable bar code. Checksums are not required. If you have your choice, Code 128 is generally the best all-around choice you can use.

Code 39
Code 39 (or Code 3 of 9) is the most common bar code in use for custom applications. It is popular because it can support both text and numbers (A‹Z, 0‹9, +,-, ., and), it can be read by almost any bar code reader in its default configuration, and it is one of the oldest of the modern bar codes. Code 39 is a variable-width bar code, and it can support any number of characters that the reader can scan. Code 39 is specified in many military and government specifications.

Interleaved 2 of 5
Also known as I2 of 5, this is a numeric-only bar code that prints out a little larger than the UPC-A bar code when 10 digits are encoded. This symbology has the flexibility to encode any even number of digits. If you have an odd number, a leading zero is added. This bar code is an excellent candidate for numeric-only applications, and it is the best symbology to use for fixed-mount readers. Because Interleaved 2 of 5 is prone to substitution errors, you should always use a checksum.

UPC (Universal Product Code)
UPC is the standard bar code for items for sale to the public. It is the code seen on items at the local supermarket. UPC-A is a fixed-length, numeric-only bar code. It contains 1 digit for a system number, 5 digits for the manufacturer number, 5 digits for the product number, and one checksum digit. This symbology contains the same information as UPC-A, except that at least four zeros are suppressed. Only tags with the system character of 0 can be encoded with this symbology. UPC-A and UPC-E codes have an automatic checksum. Interleaved 2 of 5 is almost as dense and does not have the format considerations.

Code 93 and Extended Code 93
Code 93 and Extended Code 93 are compressed versions of Code 39 and Extended Code 39. This symbology supports the same characters as Code 39, but in a smaller character width. This is a more difficult symbology to read, and many readers do not support it. Both Code 93 and Extended Code 93 have automatic checksums.

UCC 128
This bar code is a 19-digit, fixed-length bar code that uses Code 128 C to generate the bar code. This bar code is specifically used on shipping containers by those who ship items with UPC codes. UCC 128 has automatic checksums

Codabar
Codabar bar codes can include numeric characters, six punctuation characters (-$:/.+), and spaces. There are also four special start/stop characters, which are A, B, C, and D. Codabar is useful for encoding dollar figures and mathematical figures. These bar codes are slightly larger than Interleaved 2 of 5 bar codes. Codabar requires start and stop characters. The Codabar symbology is self-checking, but you can use a mod 16 or mod 10 checksum.

EAN
The EAN-13 code is used for overseas applications where a country code is required. The UPC-A symbology is actually a subset of the EAN/JAN-13 symbology. This bar code is composed of 2 numbers for the country code, 10 numbers for the data characters, and a checksum. The checksum is generated automatically. The EAN/JAN-8 code is also used for overseas applications where a country code is required. This is similar to the EAN-13 except that only 5 numbers are used.

2D (Two-Dimensional) Bar Code Symbologies
A 2D bar code symbology allows vast amounts of data on a single bar code by storing data in 2 dimensions. A common demonstration of the technology is a single bar code no larger than a standard UPC bar code that contains the entire Gettysburg Address. Some common 2D bar code symbologies include PDF 417, DataMatrix Code, and Maxi Code