||Wikimedia Commons has media related to 1666.
1666 (MDCLXVI) was a common year starting on Friday (dominical letter C) of the Gregorian calendar and a common year starting on Monday (dominical letter G) of the Julian calendar, the 1666th year of the Common Era (CE) and Anno Domini (AD) designations, the 666th year of the 2nd millennium, the 66th year of the 17th century, and the 7th year of the 1660s decade. As of the start of 1666, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923. This is the first year to be designated as an Annus mirabilis, in John Dryden's 1667 poem so titled, celebrating England's failure to be beaten either by the Dutch or by fire. It is the only year to contain each Roman numeral once in descending order (1000(M)+500(D)+100(C)+50(L)+10(X)+5(V)+1(I) = 1666).
- July – The town of Piteå in Sweden is completely burned by a large fire.
- August 4 (July 25 Julian calendar) – Second Anglo-Dutch War – St. James's Day Battle: The English fleet under Prince Rupert of the Rhine and George Monck, 1st Duke of Albemarle, defeats the Dutch off the North Foreland of England.
- August 19–20 (August 9–10 Julian calendar) – 'Holmes's Bonfire': Rear Admiral Robert Holmes leads an English raid on the Dutch island of Terschelling, destroying 150 merchant ships in the Vlie estuary, and pillaging the town of West-Terschelling.
- September 2–5 – Great Fire of London: A large fire breaks out in the City of London in the house of a baker on Pudding Lane near London Bridge. The fire destroys more than 13,000 buildings including Old St Paul's Cathedral but only six people are known to have died, whilst at least 80 were left destitute and homeless. The re-surveying of property is credited with giving both cartography and the practices of surveying a leg up, as well as resulting in the modern definition by John Ogilby of the statute mile as 1760 yards.
- September 6 – Cestui que Vie Act 1666 passed by the Parliament of England to provide for disposal of the property of missing persons.
- September 7 – Samuel Pepys describes the aftermath of the Great Fire of London in his diary and details the city in ruins.
- September 16 – Apostasy of Sabbatai Zevi in Istanbul.
- December 12 – A sobor (church council) of the Russian Orthodox Church deposes Patriarch Nikon of Moscow, but accepts his liturgical reforms. Dissenters from his reforms, known as Old Believers, continue to this day.
- December 22 – The French Academy of Sciences, founded by Louis XIV, first meets.
- Mughal forces of Emperor Aurangzeb, in alliance with the Portuguese, under Shaista Khan and his son Buzurg Umed Khan expel the Arakans from the Bengal port city of Chittagong, renaming the city as Islamabad.
- Moulai al-Rashid conquers Fes, marking the beginning of Morocco's Alaouite dynasty which will continue in power into the 21st century.
- Isaac Newton uses a prism to split sunlight into the component colours of the optical spectrum, assisting understanding of the nature of light. He also develops differential calculus. His discoveries this year lead to it being referred to as his Annus mirabilis.
- Lund University is founded in Lund, Sweden.
- Dutch artist Johannes Vermeer paints The Art of Painting, his largest and most complex work.
- The first completed printed Bible translation into Armenian, Astuacašunč hnoc' ew noroc' ktakaranac' ("Oskanean Bible"), is published in Amsterdam, edited by Bishop Oskan Yerevantsi.
- Jean Talon completes a census of New France, the first census in North America.
- February 1 – Marie Thérèse de Bourbon, Princess of Conti and titular queen of Poland (d.1732)
- February 9 – George Hamilton, 1st Earl of Orkney, British soldier (d. 1737)
- March 15 – George Bähr, German architect (d. 1738)
- May 14 – Victor Amadeus II of Sardinia (d. 1732)
- July 10 – John Ernest Grabe, German-born Anglican theologian (d. 1711)
- July 23 – Thomas Parker, 1st Earl of Macclesfield (d. 1732)
- August 13 – William Wotton, English scholar (d. 1727)
- September 5 – Gottfried Arnold, German church historian (d. 1714)
- September 6 – Tsar Ivan V of Russia (d. 1696)
- November 12 - Mary Astell, feminist writer (d. 1731)
- December 26 – Guru Gobind Singh, 10th Guru of Sikhism, Founder and Chief General of the Khalsa Army, social reformist, poet, and revolutionary (d. 1708)
- date unknown – Arthur Chichester, 3rd Earl of Donegall (d. 1706)
- January 20 – Anne of Austria, queen of Louis XIII of France and regent (b. 1601)
- January 22 – Shah Jahan, Mughal Emperor of India (b. 1592)
- January 24 – Johann Andreas Herbst, German composer (b. 1588)
- January 28 – Tommaso Dingli, Maltese architect and sculptor (b. 1591)
- February 24 – Nicholas Lanier, English composer (b. 1588)
- March 1 – Ecaterina Cercheza, Princess consort of Moldavia (b. 1620)
- June 16 – Sir Richard Fanshawe, British diplomat and translator (b. 1608)
- June 30 – Alexander Brome, English poet (b. 1620)
- July 5 – Albert VI, Duke of Bavaria (b. 1584)
- August 6 – Tjerk Hiddes de Vries, Frisian naval hero and commander (of wounds received at St. James's Day Battle) (b. 1622)
- August 15 – Johann Adam Schall von Bell, German Jesuit missionary (b. 1591)
- August 26 – Frans Hals, Dutch painter (b. 1580)
- October 29 – Edmund Calamy the Elder, English Presbyterian leader (b. 1600)
- October 29 – James Shirley, English dramatist (b. 1596)
- December 9 – Giovanni Francesco Barbieri (Guercino), Italian painter (b. 1591)
- December 26 – Alexandrine von Taxis, German Imperial General Post Master (b. 1589)
- date unknown