The 1906 Intercalated Games or 1906 Olympic Games (Greek: Μεσολυμπιάδα, romanized: Mesolympiada, lit. 'Mesolympics'), held from 22 April 1906 to 2 May 1906, was an international multi-sport event that was celebrated in Athens, Kingdom of Greece. They were at the time considered to be Olympic Games and were referred to as the "Second International Olympic Games in Athens" by the International Olympic Committee (IOC). However, the medals that were distributed to the participants during these Games were later not officially recognised by the IOC and are not displayed with the collection of Olympic medals at the Olympic Museum in Lausanne, Switzerland.

The 1906 Games are noted for their influence on the Olympic tradition and the records broken during these Games are recorded in history, but are no longer considered part of the Olympic records. 894 athletes from 20 nations competed in this competition. The idea behind the Intercalated Games was to have an Olympics in Greece every four years, but this would be the first and last. The idea was not pursued further and is sometimes called the "forgotten Games" in the context of the Olympics. The next Olympic Games would be the 1908 Summer Olympics in London, and the next time the Olympic Games would return to Greece was 98 years later in 2004 also in Athens.

The Intercalated Olympic Games were to be a series of International Olympic Games halfway between what is now known as the Games of the Olympiad. This proposed series of Games, intercalated in the Olympic Games cycle, was always to be held in Athens and was to have equal status with the international Games. However, the only such Games were held in 1906.

One reason for the Games in 1906 was to celebrate the tenth anniversary of the 1896 Games.

The first Intercalated Games had been scheduled by the International Olympic Committee in 1901 as part of a new schedule, where every four years, in between the internationally organised Games, there would be Intermediate Games held in Athens.

This was a compromise; after the successful Games of Athens 1896, the Greeks suggested they could organise the Games every four years. Since they had the accommodation and had proven they could hold well-organised Games, they received substantial public support. However, Pierre de Coubertin, the founder of the International Olympic Committee, opposed this, as he had intended for the first Games to be in Paris in 1900. After Paris had lost the première Olympics, De Coubertin did not want the Games to be permanently hosted elsewhere.

The 1900 Games were overshadowed by the Exposition Universelle, whose organising committee disagreed with De Coubertin's ideas to such an extent that he resigned. The organisation of the 1900 Games was haphazard by today's standards, and although some events, such as archery, drew widespread attention, many others were poorly attended. Historians' opinions still differ over which events should be considered "Olympic".

Consequently, the IOC supported the Greek idea by granting them a second series of quadrennial Games in between the first series. All of the Games would be International Olympic Games: the difference was that half of them would follow De Coubertin's idea of "organisation internationale", while the other half would follow the Greeks' idea of a permanent home with the Committee of the Olympic Games, as it was then known, as experienced organisers.