Together with the Casón del Buen Retiro, this is the most characteristic building that still remains of the great palatial set of buildings known as the Real Sitio y Palacio del Buen Retiro. Built between 1630 and 1635 it housed the best paintings, most of them today housed in the Museo del Prado. The Salón got its name from the crests of the 24 kingdoms belonging to the Spanish Monarchy under Felipe IV that are painted there. It is also called Museo del Ejército (the Army Museum), after the institution that housed their collections there until the recent transfer to Alcazar de Toledo.

It was initially conceived as a stage for the kings to watch the theatrical performances held in the courtyard. When it was decided to turn Buen Retiro into a real palace, it was also used as a throne room. Numerous windows provide the salon with natural light, it is furnished with jasper tables decorated with silver lions and the vaulted ceiling is covered with frescoes depicting golden grotesques. The walls were full of pictorial decorations with political symbolism, whose ultimate goal was the praise of King Felipe IV.

From 1884 onwards, the Salón de Reinos housed the Army Museum, which has now been moved to the Alcazar-Fortress in Toledo, in order to recover its past ornamental splendour and incorporate it into the expansion of the Prado Museum, of which it has been a part since 2015.

Currently, it is closed to the public while the interior is being refurbished.

Following the approval by the Council of Ministers of a line of credit to renovate and refurbish the Salón de Reinos, at the Prado Museum, Madrid City Council and the Prado signed an agreement in October 2021 to work together to integrate the Salón de Reinos architecturally and technically into the rest of the Prado Museum complex.

Consequently, the area immediately surrounding the Salón de Reinos will be redeveloped, and a maintenance and facilities tunnel will be built underground between the south wall of the Salón de Reinos and the north wall of the Casón del Buen Retiro, as well as the north staircase, and the staircase and south ramp providing access to the refurbished building. Exempt sculptures on the north terrace of the Salón de Reinos building will also be restored, two of which are owned by Madrid City Council.

The works are expected to be completed in 2025.