An ISIN consists of several parts.
Alphanumeric ISIN
An ISIN is an alphanumeric, twelve digit code. With the assignment of an ISIN it is secured that a security can be identified uniquely worldwide.
An ISIN consists of prefix, base number and check digit.
Example:
Prefix
The prefix represents the two-letter country abbreviation (using ISO 3166 codes) designating the country whose national numbering agency assigned the ISIN in question.
Base number
The base number has nine digits and it can be composed of letters and numerics. If this national code has fewer than nine digits it is preceded by the appropriate numbers of zeros.
Check digit
The check digit is calculated using a special algorithm which is known as modulus 10 "double-add-double".