The Puerta del Sol (Spanish: [ˈpweɾta ðel ˈsol], English: "Gate of the Sun") is a public square in Madrid, one of the best known and busiest places in the city.

Between the 17th and 19th centuries, the area was an important meeting place: as the goal for the couriers coming from abroad and other parts of Spain to the Post Office, it was visited by those eager for the latest news.

The stairs to the Saint Philip church at the square were known as the Gradas de San Felipe, and were among the most prolific mentideros de la Corte (this Spanish idiom sounds as "lie-spreaders of the Court", but it is related with the verb mentar, "to say about someone", not mentir, "to lie", so it is more appropriately translated as "places of the City where people gossip").

The demonstrations included camping in the middle of the plaza (@acampadasol), which began on 15 May 2011 amidst the election campaign for city halls and Autonomous Communities governments and which was fueled by social media, particularly Twitter and Facebook.

[1] During New Year's Eve 2018–2019, the clock of the Puerta del Sol for the first time in history rang the bells according to the schedule of the Canary Islands.

There are two commemorative plaques in the front of the Royal House of the Post Office: one is devoted to the neighbours of Madrid who rose up against the Napoleonic invasion of Spain on May 2, 1808; the other one is a memorial of the victims of the March 11th, 2004 terrorist attacks.

Also on its south side, the square holds a mounted statue of Charles III of Spain, nicknamed "el rey alcalde" ("the mayor-king") due to the extensive public works program he set in motion.

The kilómetro cero is a plaque on the ground directly north of the Post Office serving as the symbolic center of Spain, and the point from which kilometer distances are numbered in the Spanish road system.

The lateness of the construction was in part due to the discovery of the remains of the Church of Our Lady of Good Success during the excavation of the main chamber.

The area remains active late into the night and early morning since nearby bars and dance clubs often only start entertainment at 1 am.