Caltanissetta (Sicilian: Cartanissètta) is a city and municipality in the autonomous region of Sicily in Italy, and the capital of the free municipal consortium of Caltanissetta. In 2025, it has a population of 58,045.

The earliest inhabitants of the surrounding territory were the Sicani, who established various settlements as early as the 19th century BC. However, the modern city was likely founded in the 10th century during the Islamic period in Sicily, when the name "Caltanissetta" is believed to have originated, though alternative theories have been proposed over time. Under the Normans, it was transformed into a feudal holding, and after various transitions, it came under the control of the Montcada of Paternò in 1405. This noble family governed the County of Caltanissetta until 1812, leaving behind the Baroque-style Palazzo Moncada, constructed in the 17th century.

From the 19th century onward, Caltanissetta experienced significant industrial growth due to its extensive sulfur deposits, establishing it as a key mining center. Its prominence in the sulfur industry earned it the nickname "world sulfur capital," and in 1862, it became home to Italy's first mining institute, the Sebastiano Mottura Institute. During the 1930s, despite fascist censorship, the city enjoyed a period of cultural vibrancy, leading Leonardo Sciascia to describe it as a "little Athens." After World War II, the mining sector declined, plunging the local economy into crisis. Today, the city's economy relies predominantly on the tertiary sector.

The toponym "Caltanissetta" (with an obsolete variant, Caltanisetta) derives from the Arabic Qalʿat an-nisāʾ, literally "fortress of the women" or "castle of the women." This name was recorded by the Arab geographer Muhammad al-Idrisi in 1154 in his Book of Roger. Confirmation of its Arabic origin appears in an 11th-century text by Goffredo Malaterra, who wrote:

—Goffredo Malaterra, De rebus gestis Rogerii Calabriae et Siciliae comitis et Roberti Guiscardi ducis fratris eius

The reason behind this designation remains unclear. The notion that the Pietrarossa Castle served as a harem for the Emir of Palermo lacks evidence, given the fortress's military character. According to local historian Rosanna Zaffuto Rovello, the name may reflect a situation in which the men, who worked in the distant fields, lived away from the village, leaving it predominantly inhabited by women.

Scholar Luigi Santagati suggests the toponym indicates an unconfirmed pre-existing Byzantine settlement. He posits that nisāʾ ("woman" in Arabic) might be a corruption of Nissa, an Anatolian city from which Byzantine stratioti originated. These soldiers may have built the Pietrarossa Castle and a nearby village named Nissa, now the Angeli district. Following Arab conquest, the prefix Qalʿat ("castle") was added, akin to the renaming of Henna (modern Enna) as Qasr Yannae, later Castrogiovanni, and other localities where Byzantine names were adapted or integrated.

With the Norman arrival in the 11th century, the city adopted Latinized forms like Calatenixet (per Malaterra) or Calatanesat, a transliteration from al-Idrisi's Arabic. By the late 12th century, historian Hugo Falcandus in his Liber De Regno Sicilie refers to it as Caltanixettum, the official Latin precursor to its modern name.