1604 (MDCIV) was a leap yearstarting on Thursday of the Gregorian calendarand a leap year starting on Sunday of the Julian calendar, the 1604th year of the Common Era (CE) and Anno Domini (AD) designations, the 604th year of the 2ndmillennium, the 4th year of the 17thcentury, and the 5th year of the 1600s decade. As of the start of 1604, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.

• January 14 – Hampton Court conference with James I of England, the Anglican bishops and representatives of Puritans
• September 20 – Capture of Ostend by Spanish forces under Ambrosio Spinola after a three-year siege.
• October 9 – Supernova 1604 is observed. As of this writing, this was the last supernova to be observed in the Milky Way.
• November 1 – At Whitehall Palace in London, the William Shakespeare tragedy Othello is presented for the first time.
• The Sikh Holy Scripture Guru Granth Sahib is compiled and edited by Guru Arjan .
• Luis Váez de Torres is the first European to sail through the Torres Strait.
• France begins settling Acadia, first successful French North American colony
• France begins settling French Guiana.
• England concludes the Treaty of London with Spain, ending its involvement in the Eighty Years' War.
• Peter Blundell founds Blundell's School in Tiverton, England.
• Za Dengel deposed as Emperor of Ethiopia by Za Sellase, who restores his cousin Yaqob.
• The first known English Dictionary to be organized by alphabetical ordering was published.