First of all, to understand its history, it's best to know that the National Galleries of Scotland is a non-departmental executive public body that controls Scotland's three national galleries and thus shapes one of Scotland's national collections.
The National Galleries of Scotland began to take shape in 1859, when the National Gallery, now known as “the National”, designed by William Henry Playfair, opened its doors to the public for the first time that same year. At the time, the building home to the National was shared with the Royal Scottish Academy.
After only a few years, the success of the gallery and the growth of the National Gallery's collection of paintings were such that the National Portrait Gallery was founded in 1882 in response to this strong demand and opened to the public in 1889.
Changes to this public body continued over the years. In 1906, it was agreed that the National Gallery did not have enough space to display all of its collections and that the entire building, which had until now been shared, should be reserved exclusively for it. The Royal Scottish Academy was, thus, relocated to the building opposite.
It was then in 1959 that a brand new project was launched. A third gallery opened, the Scottish National Gallery of Modern Art, at Inverleith House in Edinburgh's Royal Botanic Garden. In its early days, it consisted mainly of works of art dating from after 1900 and moved from the National Gallery. It was from 1960 onwards that the gallery acquired new objects to complete its collection.
However, when the Modern Art Gallery began to build up new collections of modern art, its building at the time became too small to accommodate them all. So the gallery moved to Belford Road, a former school. The collection has grown steadily over the years, to the point where a second part of the modern art gallery was created in 1999, called Gallery of Modern Art Two, or Dean Gallery. The latest is now located opposite Gallery of Modern Art One in a former orphanage.