Retail symbologies
It is worth noting that there are different barcode symbologies used on products in Europe compared to the USA.
European Retail Industry
In Europe and the UK you will nearly always see EAN-13 codes on supermarket and retail products. This number is assigned by the International Article Numbering Association (originally the European Article Numbering Association) which is why no two products will ever have the same EAN code.
EAN-8 codes are used where there is limited space for example chewing gum packets and on cigarettes. EAN8 can also be used to encode the GTIN-8 codes from the GS1 system.
USA Retail Industry
In the USA you will commonly see Universal Product Codes or UPC-A and UPC-E codes used to track trade items in stores from food products to books and newspapers. If you are not supplying or working in that environment it is unlikely you will require this type of code.