ISIN

An ISIN is structured as a two-letter ISO country prefix, a nine-character national security number (the NSIN, e.g. a CUSIP in the US), and a single check digit computed with the Luhn algorithm. Because a ticker like RIO can mean different companies on different exchanges, the ISIN is the safe join key for normalising filings across 43 regulators into one company record.

• Example: US0378331005 is Apple Inc. (US prefix, 037833100 CUSIP, check digit 5).
• The ISIN identifies the security, not the listing; the same ISIN can have several tickers (one per venue).