Tatoi (Greek: Τατόι, pronounced [ta.ˈto.i]) was the summer palace and 42 km (10,000 acres) estate of the former Greek royal family. The area is a densely wooded southeast-facing slope of Mount Parnitha, and its ancient and current official name is Dekeleia. It is located 27 km (17 mi) from the city centre of Athens and 2.5 km (2 mi) from Kifissia.

King George I purchased the estate in 1872, purchasing it with private funds he had brought from Denmark.

In July 1916, an arson attack ravaged Tatoi Palace. The royal family barely escaped the flames. Among the palace personnel and firefighters who arrived to deal with the blaze, sixteen people were killed.

During the Republican regime in the 1920s, most of the estate was confiscated from its owners. Around 1929-1930 the government allowed Dimitrios Gaziadis to film the movie The Apaches of Athens (1930) at the lavish estate. In 1936, it was returned to King George II of the Hellenes following the monarchy's restoration.

During the Second World War, when the King was in exile and Greeks suffered considerable hardships under German occupation, the woods at Tatoi were chopped down for fuel and corpses were buried in shallow graves.

King George II regained possession of the estate in 1946. It passed down as private property to King Constantine II until 1994, when the royal estates were confiscated by the government of Andreas Papandreou.

In 1973, the property was abandoned completely. Lack of funding resulted in the cows and horses dying of starvation in the stables. The buildings were subject to vandalism and looting, resulting in significant losses. A former cowshed was filled with objects from Rododafni Castle, the mansion at Psychico, Mon Repos palace, and other royal residences. With permission of the Government, in 1993, the ex-King was able to remove nine cargo crates of objects: some of this appeared at auction at Christies in 2007. There remained 17,000 objects, including antiquities, old masters, and a life-size portrait of Queen Anne-Marie that are now in storage at the Ministry of Culture.

In June 2007, the Government of Greece said it intended to turn the former palace and grounds into a museum. However, it was reported in September 2012 that the government now intended to sell the palace and its estate in the face of mounting financial pressure. Founded in 2012, the "Friends of Tatoi Association" has set itself the goal to restore the former royal estate and convert it to a museum and public venue, while facing political indifference and lack of money.

In 2015, ten cars which were kept in the former royal estate of Tatoi, were designated as cultural monuments by the Central Council for Modern Monuments (ΚΣΝΜ). However, the cars, as well as the carriages (which were not included in the decision) remained in the ruins, with parts of the roof falling on the cars in 2016. However, as of 2020, the cars and carriages have now been removed and restored as part of greater restoration efforts by the Greek government.

For several years, the Greek government had no planned efforts for preservation of the Tatoi Palace, neighbouring buildings and the natural area around the Tatoi, and the estate suffered from extensive age and weather damage. The Greek state had renamed the area as metropolitan area. A political idea to convert the former royal estate to a private winery or a resort with restaurants and barbecue was met with criticism by private persons and organisations, who feared it could erase the historical elements of the property, and who preferred to open Tatoi as a museum for the public. The former royal estate of Polydendri is also completely abandoned, and the buildings are in a state of decay.

In late 2019, the Greek culture ministry moved ahead with plans to finally restore the palace. After approximately a year of conservation work had been undertaken, the Greek government announced that the estate would become a mixed-use development after the completion of restoration. Plans are centered on the conversion of the main house into a museum of the royal family, as well as the construction of a new luxury hotel and spa. The 2021 forest fires were catastrophic for the estate: 16,997 hectares (42,000 acres) were burnt, with a fire breaking out in the Palace itself. While it was saved, two adjoining storage containers containing objects were destroyed. The area of the Royal Cemetery burned, but the Mausoleum and the Church of the Resurrection were saved. A number of estate buildings, including the Directorate building (which was being used to store furniture), the caretaker's house, the Telegraph Office and Sturm House, were lost.

Following the death and funeral of Constantine II, it was announced by Lina Mendoni, the Minister of Culture and Sports, that the government intended to have Tatoi transformed into a museum by 2025. Points of interest are renovating the exterior and tidying up the royal gardens. The project comes following clean-up crews' efforts to clean Tatoi Palace and its surroundings for the burial of Constantine II. The forest started recovering by 2024 and plans were announced for the restoration of the palace gardens. The renovations are expected to be completed by late 2025.

Tatoi Royal Cemetery is a private cemetery located on the south end of the estate in a large wooded area.

Buried in the Tatoi Royal Cemetery are:

1. Princess Olga of Greece and Denmark (1880–1880)
2. Princess Alexandra of Greece and Denmark, Grand Duchess of Russia (1870–1891) – (wife of Grand Duke Paul Alexandrovich of Russia)
3. George I of Greece (1845–1913)
4. Alexander of Greece (1893–1920)
5. Constantine I of Greece (1868–1923)
6. Grand Duchess Olga Constantinovna of Russia, Queen of the Hellenes (1851–1926) – (wife of George I of Greece)
7. Princess Sophia of Prussia, Queen of the Hellenes (1870–1932) – (wife of Constantine I of Greece)
8. Prince Nicholas of Greece and Denmark (1872–1938)
9. Prince Christopher of Greece and Denmark (1888–1940)
10. Princess Maria of Greece and Denmark, Grand Duchess of Russia (1876–1940) – (wife of Grand Duke George Mikhailovich of Russia)
11. Prince Andrew of Greece and Denmark (1882–1944) (father of the Duke of Edinburgh, husband of Queen Elizabeth II)
12. George II of Greece (1890–1947)
13. Princess Françoise of Orléans (1902–1953) – (wife of Prince Christopher of Greece and Denmark)
14. Grand Duchess Elena Vladimirovna of Russia (1882–1957) – (wife of Prince Nicholas of Greece and Denmark)
15. Prince George of Greece and Denmark (1869–1957)
16. Princess Marie Bonaparte (1882–1962) – (wife of Prince George of Greece and Denmark)
17. Paul of Greece (1901–1964)
18. Aspasia Manos, Princess of Greece and Denmark (1896–1972) – (wife of Alexander of Greece)
19. Princess Frederica of Hanover, Queen of the Hellenes (1917–1981) – (wife of Paul of Greece)
20. Princess Katherine of Greece and Denmark, Lady Katherine Brandram (1913–2007) – (daughter of Constantine I of Greece, wife of Richard Brandram)
21. Constantine II of Greece (1940–2023)
22. Prince Michael of Greece and Denmark (1939–2024)

A mausoleum was built to house the bodies of Constantine I, Sophia and Alexander, seen in the image above. The remaining members are buried in tombs with crosses near the Resurrection Church.

Princess Alexandra of Greece and Denmark, Queen of Yugoslavia (1921–1993) was buried here from 1993 until 2013, when her remains were exhumed and returned to Serbia, where they were reburied at Oplenac in 2013.

Tatoi has a hot-summer Mediterranean climate (Csa) with hot, dry summers and cool, rainy winters. The lowest temperature ever recorded is −8.9 °C (16.0 °F) on 9 January 2019.

Tatoi was until 2021 one of the areas in the Athens Metropolitan Area (the other one was Elefsina) which held the record of the highest ever officially recorded temperature in Europe for 44 years with a reading of 48.0 °C (118.4 °F) on 10 July 1977.

• Palataki (Thessaloniki)

• Kardamitsi-Adami, Maro (2009). Palaces in Greece. Melissa Books. ISBN 978-960-204-289-2.
• Kostas M. Stamatopoloulos, The Chronicle of Tatoi, Kapon Editions, Athens, 2015
• Kostas M. Stamatopoloulos, Tatoi: Tour In Time And Space, Kapon Editions, Athens, 2015
• Symboulidis, Haris (15 February 2020). "Οι Απάχηδες Των Αθηνών" [The Apachis of Athens] (in Greek). Athens, Greece: Avopolis. Archived from the original on 23 March 2023. Retrieved 23 March 2023.

• Van der Kiste, John (1994). Kings of the Hellenes: The Greek Kings, 1863–1974. Dover, New Hampshire and Stroud, Gloucestershire: Sutton Publishing. ISBN 0-7509-0525-5.

• Tatoi Palace Picture Gallery by photographer Christos Gorezis
• Tatoi Estate: from extravagance to abandonment
• Tatoi Friends Association

38°09′45.83″N 23°47′37.28″E / 38.1627306°N 23.7936889°E / 38.1627306; 23.7936889