1599 (MDXCIX) was a common yearstarting on Friday of the Gregorian calendarand a common year starting on Monday of the Julian calendar, the 1599th year of the Common Era (CE) and Anno Domini (AD) designations, the 599th year of the 2ndmillennium, the 99th year of the 16thcentury, and the 10th and last year of the 1590s decade. As of the start of 1599, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.

• January 8 – The Jesuit educational plan known as the Ratio Studiorum is issued.
• June 20 – The Synod of Diamper is convened.
• August 15 – First Battle of Curlew Pass: Irish forces defeat the English.
• September 21 – The first reported performance of Shakespeare's Julius Caesar at the Globe Theatre in London, is recorded by Swiss traveller Thomas Platter the Younger.
• * October 18 – Battle of Sellenberk: Michael the Brave, Prince of Wallachia, defeats the army of Andrew Báthory near Șelimbăr, leading to the first recorded uniting of the Romanians.