EAN is the code most commonly used for numbering retail products.
EAN International issues 13 digit numbers, each comprising a 2 digit country code (known as flag), a 5 or 7 digit manufacturers number, a 3 digit product number and last number being a check digit. The 13 digit symbol can also take on a 2 or 5 digit add on commonly known as the addendum.

EAN 8 is a separate short number containing only 8 digits which is issued in cases where space is limited. This short form is often chosen for in-house numbering schemes.
The size of a bar code is governed by its Magnification Factor (M.F.), the standard or Nominal size being 100%. For the EAN symbol magnification factors between 80% and 200% are permitted.
EAN codes have a nominal height, which varies in proportion to the magnification factor; although in practice it is often adjusted. Shortening of the code height is permitted but not recommended depending on the point of sale the bar code may not be accepted due to high speed scanners now implanted.

Trade Units was initially developed for use on outer cartons or cases containing a number of identical retail items. The materials and the methods of printing used for bulk packaging could not meet the specifications of EAN/UPC bar coding. A system that was more tolerant of print variation was required - hence the adoption of the Trade Unit symbology was founded.

ISBN (International Standard Book Numbering)
ISBN (International Standard Book Numbering) (10 Digit & 13 Digit ISBN)
ISBN’s are printed on books. The number is encoded in an EAN symbol. It is identified by a three digit prefix. This is currently 978 or 979 followed by a 9 digit or 12 digit book number followed by the check digit.

ISSN’s are printed on magazines and periodicals. The number is encoded in an EAN symbol. It is identified by the 3 digit prefix 977. ISSN contains 13 digits followed by an optional 2 or 5 digit add on commonly known as the addendum.

UPC is the code widely used for numbering retail products in the USA & Canada. The 12 digit number is encoded in a 13 digit EAN symbol; the two numbering systems having been designed to prevent conflict. UPC codes are compatible with EAN scanning systems, but UPC systems expecting no more than 12 digit numbers cannot use EAN symbols.

Code 39 is a bar code which includes a complete series of alphanumeric characters, unique start and stop characters and seven special characters. It consists of three wide elements out of nine (name Code 39). These nine elements are composed of five bars and four spaces each and can have up to 64 characters.