The Río de la Plata (Spanish pronunciation: [ˈri.o ðe la ˈplata], River of Silver)—sometimes rendered River Plate in British English and the Commonwealth, and occasionally rendered [La] Plata River in other English-speaking countries—is the river and estuary formed by the confluence of the Uruguay River and the Paraná River on the border between Argentina and Uruguay. It is a funnel-shaped indentation on the southeastern coastline of South America, about 290 kilometres (180 mi) long.

The Río de la Plata widens from about 2 kilometres (1.2 mi) at the inner part to about 220 kilometres (140 mi) at its mouth. It forms part of the border between Argentina and Uruguay, with the major ports and capital cities of Buenos Aires and Montevideo on its western and northern shores, respectively. The coasts of the Río de la Plata are the most densely populated areas of Argentina and Uruguay.

Some geographers consider the Río de la Plata a gulf or marginal sea of the Atlantic Ocean, while others consider it a river. For those who regard it to be a river it is the widest in the world, with a maximum width of about 220 kilometres (140 mi) and a total surface area of about 35,000 square kilometres (14,000 sq mi).

La Plata (English: The Silver) is the capital city of the Province of Buenos Aires, Argentina, and of La Plata partido. According to the 2001 census [INDEC], the partido has a population of 574,369 and its metropolitan area has 694,253 inhabitants. The city itself has a population of 186,524.

La Plata was planned and developed to serve as the provincial capital after the city of Buenos Aires was federalized in 1880, and it was officially founded by Governor Dardo Rocha on 19 November 1882. Its construction is fully documented in photographs by Tomás Bradley Sutton. La Plata was renamed Eva Perón City (Ciudad Eva Perón) between 1952 and 1955.

The city is home to two football (soccer) teams that play in the first division: Estudiantes de La Plata and Gimnasia y Esgrima La Plata.

Rocha decided to erect a new city to host the provincial government institutions and the planned university. Urban planner Pedro Benoit designed a city layout based on a rationalist conception of urban centers. The city has the shape of a square with a central park and two main diagonal avenues, north-south and east-west. (In addition, there are numerous other shorter diagonals.) This design is copied in a self-similar manner in small blocks of six by six blocks in length. Every six blocks, one finds a small park or square. Other than the diagonals, all streets are on a rectangular grid, and are numbered consecutively. Thus, La Plata is nicknamed "la ciudad de las diagonales" ("city of diagonals"). It is also called "la ciudad de los tilos" ("city of tilia (linden trees)") because of the large number of linden trees lining many streets and squares.