The International Database on Longevity (IDL) is the result of a concerted effort to gather demographic information on those who have lived to a validated age of 105 years or over, opening the door to accurate measurement of mortality at very old ages. IDL collates information on deaths at age 105+ from countries with reliable civil registry or equivalent systems. To ensure completeness, data collection relies on sources that systematically include all deaths that occur within a population or territory. The deaths collected in this way are then subjected to a strict age validation procedure. The recommended procedure involves verifying that the identity and birth information contained in the death certificate match those appearing on the birth certificate. However, this procedure does vary between countries (see metadata sheets). For each individual, IDL provides anonymous information on sex, date of birth, date of death, place of birth, and place of death. The database currently contains records on 18,959 individuals from 13 participating countries.