International Securities Identification Number (ISIN)

An ISIN identifies an issue of a financial instrument for processing and reporting across markets. National numbering agencies assign ISINs under ISO 6166, with the Association of National Numbering Agencies coordinating the network. The country prefix indicates the assigning jurisdiction under the standard's rules; it should not be read automatically as the issuer's domicile or the place where an instrument trades.

An instrument can have several market identifiers and trading symbols while retaining its ISIN. Conversely, an issuer may have many ISINs for different securities, classes, or issuances. Matching instruments therefore requires the instrument's terms and authoritative reference data, not a name or ticker alone. Preserve the agency's record and effective date when an ISIN is used to reconcile positions or disclosures.

Halden Therapeutics AG (fictional) has issued ordinary shares and a bond. A portfolio file lists three lines: a ticker with no exchange, an ISIN for the shares, and an ISIN for the bond. The ticker line is ambiguous, because the same symbol can denote different securities on different venues. The two ISIN lines are not: each points to one issue.

To reconcile the file with a custodian's statement, the analyst matches on ISIN, then compares the quantities and the valuation date. If the custodian reports the shares under a second ISIN, the explanation may be a corporate action, a different share class or a different line of the same issuer. The reconciliation note records which source supplied each ISIN, the date of retrieval, and the issuer's LEI where the issuer was identified. When the two ISINs differ and nothing in the sources explains why, the correct result is an open difference with both values kept, not a silent substitution of one for the other.

The ISIN is often confused with a ticker, a CUSIP or a SEDOL. A ticker is a venue-specific trading symbol that can be reused. A CUSIP is a North American identifier that frequently forms the core of a U.S. or Canadian ISIN. A SEDOL is a different national identifier used for securities in the United Kingdom and Ireland. A record that stores several of these should label each by type and source, since a bare string of nine or twelve characters invites mislabelling.

It is also confused with an issuer identifier. Two bonds of one issuer have different ISINs, and a share and a bond of the same issuer have different ISINs. Counting ISINs does not count issuers. A conclusion such as "the fund holds securities of five issuers" needs the issuer link for each ISIN, preferably an LEI with its own source, and the link should carry a date, because mergers change which issuer an outstanding issue belongs to.