Saint Peter's Square (Latin: Forum Sancti Petri, Italian: Piazza San Pietro [ˈpjattsa sam ˈpjɛːtro]) is a large plaza located directly in front of St. Peter's Basilica in Vatican City, the papal enclave in Rome, directly west of the neighborhood (rione) of Borgo. Square and basilica are named after Saint Peter, an apostle of Jesus whom Catholics consider the first Pope.

At the centre of the square is the Vatican obelisk, an ancient Egyptian obelisk erected at the current site in 1586. Gian Lorenzo Bernini designed the square almost 100 years later, including the massive Doric colonnades, four columns deep, which embrace visitors in "the maternal arms of Mother Church". A granite fountain constructed by Bernini in 1675 matches another fountain designed by Carlo Maderno in 1613.

The open space which lies before the basilica was redesigned by Gian Lorenzo Bernini from 1656 to 1667, under the direction of Pope Alexander VII, as an appropriate forecourt, designed "so that the greatest number of people could see the Pope give his blessing, either from the middle of the façade of the church or from a window in the Vatican Palace". Bernini had been working on the interior of St. Peter's for decades; now he gave order to the space with his renowned colonnades, using a simplified Doric order, to avoid competing with the palace-like façade by Carlo Maderno, but he employed it on an unprecedented colossal scale to suit the space and evoke a sense of awe.

The colossal Doric colonnades, four columns deep, frame the trapezoidal entrance to the basilica and the massive elliptical area which precedes it. The ovato tondo's long axis, parallel to the basilica's façade, creates a pause in the sequence of forward movements that is characteristic of a Baroque monumental approach. The colonnades define the piazza. The elliptical center of the piazza, which contrasts with the trapezoidal entrance, encloses the visitor with "the maternal arms of Mother Church" in Bernini's expression. On the south side, the colonnades define and formalize the space, with the Barberini Gardens still rising to a skyline of umbrella pines. On the north side, the colonnade masks an assortment of Vatican structures; the upper stories of the Vatican Palace rise above.

At the center of the ovato tondo stands the Vatican obelisk, an uninscribed Egyptian obelisk of red granite, 25.5 m (84 ft) tall, supported on bronze lions and surmounted by the Chigi arms in bronze, in all 41 m (135 ft) to the cross on its top. The obelisk was originally erected in Heliopolis, Egypt, by an unknown pharaoh.

The Emperor Augustus had the obelisk moved to the Julian Forum of Alexandria, where it stood until AD 37, when Caligula ordered the forum demolished and the obelisk transferred to Rome. He had it placed on the spina which ran along the center of the Circus of Nero. It was moved to its current site in 1586 by the engineer-architect Domenico Fontana under the direction of Pope Sixtus V; the engineering feat of re-erecting its vast weight was memorialized in a suite of engravings. The obelisk is the only obelisk in Rome that has not toppled since antiquity. During the Middle Ages, the gilt ball atop the obelisk was believed to contain the ashes of Julius Caesar. Fontana later removed the ancient metal ball, now in a Roman museum, and found only dust inside; Christopher Hibbert, however, writes that the ball was found to be solid. Though Bernini had no influence in the erection of the obelisk, he did use it as the centerpiece of his magnificent piazza, and added the Chigi arms to the top in honor of his patron, Alexander VII.

The paving is varied by radiating lines in travertine, to relieve what might otherwise be a sea of setts. In 1817 circular stones were set to mark the tip of the obelisk's shadow at noon as the sun entered each of the signs of the zodiac, making the obelisk a gigantic sundial's gnomon. Below is a view of St. Peter's Square from the cupola (the top of the dome) which was taken in June 2007.