1669 (MDCLXIX) was a common year starting on Tuesday of the Gregorian calendar and a common year starting on Friday of the Julian calendar, the 1669th year of the Common Era (CE) and Anno Domini (AD) designations, the 669th year of the 2nd millennium, the 69th year of the 17th century, and the 10th and last year of the 1660s decade. As of the start of 1669, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.