Pienza (Italian pronunciation: [piˈɛntsa]) is a town and comune in the province of Siena, Tuscany, in the historical region of Val d'Orcia. Situated between the towns of Montepulciano and Montalcino, it is considered the "touchstone of Renaissance urbanism".

In 1996, UNESCO declared the town a World Heritage Site, and in 2004 the entire valley, the Val d'Orcia, was included on the list of UNESCO's World Cultural Landscapes.

Before the village was renamed Pienza its name was Corsignano. It is first mentioned in documents from the 9th century. Around 1300 parts of the village became property of the Piccolomini family after Enghelberto d'Ugo Piccolomini had received the fief of Montertari in Val d'Orcia from the emperor Frederick II in 1220. In the 13th century Franciscans settled down in Corsignano.

In 1405 Aeneas Silvius Piccolomini (Italian: Enea Silvio Piccolomini) was born in Corsignano, a Renaissance humanist born into an exiled Sienese family, who later became Pope Pius II. Once he became Pope, Piccolomini had the entire village rebuilt as an ideal Renaissance town and renamed it Pienza ("city of Pius"). Intended as a retreat from Rome, it represents the first application of humanist urban planning concepts, creating an impetus for planning that was adopted in other Italian towns and cities and eventually spread to other European centers.

The rebuilding was done by Florentine architect Bernardo Gambarelli (known as Bernardo Rossellino) who may have worked with the humanist and architect Leon Battista Alberti, although there are no documents to prove it for sure. Alberti was in the employ of the Papal Curia at the time and served as an advisor to Pius. Construction started about 1459. Pope Pius II consecrated the Duomo on 29 August 1462, during his long summer visit. He included a detailed description of the structures in his Commentaries, written during the last two years of his life.

In 2023, Pienza faced a significant controversy when its centuries-old clock tower bells were silenced at night due to tourist complaints about noise from those staying in nearby hotels. The decision stirred debate among residents, with some expressing nostalgia for the nightly tolls that had been a part of their lives for generations.

The trapezoidal piazza is defined by four buildings. The principal residence, Palazzo Piccolomini, is on the west side. It has three stories, articulated by pilasters and entablature courses, with a twin-lighted cross window set within each bay. This structure is similar to Alberti's Palazzo Rucellai in Florence and other later palaces. Noteworthy is the internal court of the palazzo. The back of the palace, to the south, is defined by loggia on all three floors that overlook an enclosed Italian Renaissance garden with Giardino all'italiana era modifications, and views into the distant landscape of the Val d'Orcia and Pope Pius's beloved Monte Amiata beyond. Below this garden is a vaulted stable that had stalls for 100 horses.

The Duomo (Cathedral), which dominates the center of the piazza, has a facade that is one of the earliest designed in the Renaissance manner. Although the tripartite division is conventional, the use of pilasters and of columns, standing on high dados and linked by arches, was novel for the time. The bell tower, however, has a Germanic flavor as is the layout of the Hallenkirche plan, a "triple-nave" plan where the side aisles are almost as tall as the nave; Pius, before he became pope, served many years in Germany and praised the effects of light admitted into the German hall churches in his Commentari. Works of art in the duomo include five altar paintings from the Sienese School, by Sano di Pietro, Matteo di Giovanni, Vecchietta and Giovanni di Paolo. The Baptistry, dedicated as usual to San Giovanni, is located next to the apse of the church.