Square Jean-XXIII, Urban park near Notre-Dame Cathedral, Île de la Cité, Paris, France

Square Jean-XXIII is a 10,797 m² green space on the Île de la Cité, adjoining the chevet and south flank of Notre-Dame Cathedral. It is bounded by the rue du Cloître-Notre-Dame to the north, the quai de l'Archevêché to the east, the Seine parapet to the south and the parvis to the west, with gates set in its fence. A marble bust of Carlo Goldoni, sculpted by Édouard Fortini, stands in the garden.

The site was a medieval dumping ground called the motta Papellardorum, used by the canons of the Notre-Dame cloister, and became a public garden reserved for men in 1687. The Archbishop's Palace was destroyed in the anti-legitimist riots of 14–15 February 1831, and prefect Rambuteau created the new garden in 1837, completing its layout in 1844.

The square's name honours Pope John XXIII, the former Angelo Roncalli, who was apostolic nuncio in Paris from 1945 to 1953. A marble bust of Venetian playwright Carlo Goldoni, sculpted by Édouard Fortini, was placed here in 1907, given by Duke Melzi d'Eril for the Dante Society. A monument to John Paul II by Zurab Tsereteli was inaugurated on 25 October 2014.

The plaza is accessible through multiple entrances near the Notre-Dame cloister area and easy to walk through. The nearby Metro station Cité on Line 4 offers straightforward access.

The square was used as an artillery park during the Franco-Prussian War of 1870 and the Paris Commune. In 1969 a councillor proposed a lapidary museum beneath the lawns for finds from the Notre-Dame parvis excavations; the plan was never built.