UPC Codes (Universal Product Codes) consists of a 12 digit number and are required for most products sold in stores and online in the USA and Canada. The codes are good for all products except pharmaceuticals, books, and magazines. In reality, all UPC Codes should have a "0" at the front of the code to identify the Country that the code is from as being the USA or Canada ("0" is the UPC Country code for the USA and Canada). Traditionally, the "0" was dropped when the UPC code was being used in the USA and Canada because it was seen as unnecessary when being used within the two Countries since both Countries have the same Country Code. UPC Codes can usually be used successfully throughout the world while just using the 12 digit number and excluding the beginning "0". If any complications arise simply adding a "0" to the front of the code should solve any issues.
EAN Codes (European Article Numbers) consist of a 13 digit number and are required for products sold in Countries other than the United States and Canada. The Country Code of other Countries is included in the EAN number of those Countries, hence the 13 digits of the EAN Code instead of the 12 digits for the UPC Code. If the "0" (the Country Code for the USA and Canada) is placed at the beginning of a UPC Code it effectively turns the UPC Code into a 13 digit EAN Code. The Code can now be used anywhere in the world. The EAN Code would be more accurately named if it were called an "IAN" (International Article Number) but the EAN title was retained instead of renaming the code.