Siena play their home games at the Stadio Artemio Franchi. The ground's capacity is only 15,725 and is located in Siena itself, whereas its more famous namesake is located in Florence. In March 2011, A.C. Siena announced plans to move to a new stadium at Isola d’Arbia, at the southern end of the city. The 20,000 seat stadium features a unique below-ground design and was awarded an MIPIM AR Future Projects Award for 2011.
Formed in 1904 as Società Studio e Divertimento (Society for Study and Entertainment), a sports club characterized by a black and white check jersey (derived from the city of Siena coat of arms), it opened its football section, named Società Sportiva Robur, in 1908. Today the name "Robur" is widely used by the local supporters to distinguish the football team from the two basket ones, "Mens Sana" and "Virtus".
The team finally became known as Associazione Calcio Siena in 1933/1934. In 1934/1935 Siena were promoted for the first time to Serie B. In the post-war season 1945–46, Siena played in the top division of Italian football for the first time. In that season, a mixed wartime league composed of Serie A and Serie B teams was played. Some of the southern sides that took part in the top division, including Siena, were Serie B teams, while northern Serie B teams played at the second level with the Serie C teams. Therefore, although Siena played in the top division, it was not considered as having played in Serie A during that season, not having qualified for the National Round.
After 55 years spent playing in several minor leagues, Siena were promoted back to Serie B for the start of the 2000/2001 season. After enjoying a good season on 2000/2001, the following season saw Siena in serious trouble, and coach Giuseppe Papadopulo, first sacked but then recalled, was able to save the team on the last day of the season.
The following season, again with Papadopulo as head coach, Siena were promoted to Serie A for the first time proper, led by players such as Rodrigo Taddei and Pinga. It had been 58 years since their last appearance in the top division of Italian football.
In the 2003/2004 campaign, the first Serie A season in the club's history, Siena ended in a respectable 13th place.
In the 2004/05 Serie A campaign, with Luigi De Canio as head coach, Siena struggled for long periods of the season, languishing in the relegation zone for a great part of the campaign, and with the team drawing far too many games and barely recording any wins, they looked almost certain to be relegated. However, a resurgence of form towards of the end of the season gave them hope, and a 2–1 win against already relegated Atalanta on the last day saw them secure safety and an acceptable 14th place in the table.
The 2005/2006 season also saw Siena fighting hard and it successfully kept its place in Serie A. They ended the season in 17th place. For the 2006–2007 season, Mario Beretta, who led Parma in the previous season, was appointed as new head coach. He kept Siena in Serie A after a 2–1 home win against Lazio in the final matchday.
During the 2006–07 season, club chairman Paolo De Luca, who took over in 2001 and helped the club to their first historical Serie A promotion, started talks to sell AC Siena to a conglomerate of Tuscan businessmen led by Giovanni Lombardi Stronati, president of Valle del Giovenco. The bid was finalized on 30 March 2007, one day before De Luca died after a long illness.
The club also explored the possibility of changing its denomination in order to include the name of their main sponsor, Monte dei Paschi di Siena. On 9 July 2007 the club announced it had changed their denomination to A.C. Siena Montepaschi. However, the name change needed to be accepted by the Italian Football Federation in order to become official: After the refusal by FIGC, this idea was abandoned.
The club was then acquired by Massimo Mezzaroma, with Valentina Mezzaroma as vice-president. On 7 May 2011, A.C. Siena were once again promoted to the Serie A after finishing in the runner-up spot in the 2010-11 Serie B. The club's stint into the top flight lasted two season, as they were relegated after ending the 2012-13 Serie A in nineteenth place.