1909 (MCMIX) was a common year starting on Friday of the Gregorian calendar and a common year starting on Thursday of the Julian calendar, the 1909th year of the Common Era (CE) and Anno Domini (AD) designations, the 909th year of the 2nd millennium, the 9th year of the 20th century, and the 10th and last year of the 1900s decade. As of the start of 1909, the Gregorian calendar was 13 days ahead of the Julian calendar, which remained in localized use until 1923.

British supercentenarian Ethel Caterham is the last surviving person who was born in 1909.