ISIN and SEDOL codes are used to uniquely identify investments. ISINs are an international standard, they have 12 digits and are alphanumeric, beginning with two letters representing the country of registration.
The stock exchange daily official list (SEDOL) is a seven-character identification code. Many investments are listed on multiple exchanges, so the SEDOL is a way of not only identifying what the security is, but it also tells us which listing we are looking at. If a security is listed on 5 different exchanges, it will have 5 different SEDOL codes.