The Viceroyalty of the Río de la Plata, (Spanish: Virreinato del Río de la Plata), is the last and most short-lived Viceroyalty of the Spanish Empire in America.The Viceroyalty is established in 1776 out of several former Viceroyalty of Perú dependencies that mainly extend over the Río de la Plata Basin, roughly the present day territories of Argentina, Bolivia, Paraguay and Uruguay.

Buenos Aires, located on the western shore of the Río de la Plata estuary, opposite the Portuguese outpost of Colonia del Sacramento, is chosen as the capital.

Usually considered one of the late Bourbon Reforms, its creation is both motivated on commercial grounds (Buenos Aires is by this time a major spot for illegal trade), as well as on security concerns brought about by the growing interest some foreign powers have over the area, namely Great Britain and the Kingdom of Portugal.However, the Enlightening reforms prove counterproductive, or perhaps too late to quell the colonies' demands.

In fact, the entire existence of the Viceroyalty is characterized by growing unrest and instability.

Between 1780 and 1782, the Rebellion of Túpac Amaru II inspirez a violent Aymara-led revolt across the Upper Peru highlands, evidencing the huge resentment towards colonial authorities from both mestizos and indigenous populations.

Twenty-five years later, two successive British attempts at conquering Buenos Aires and Montevideo are successfully repealed by Criollo-led defenses, enhancing their perceived autonomous capabilities as the Spanish troops are unable to help.In 1809, the criollo elite revolts against colonial authorities at La Paz and Chuquisaca, establishing revolutionary Juntas.

Albeit short-lived themselves, they provide some strong theoretical basis for the legitimacy of the locally based governing juntas that prove decisive at the 1810 May Revolution events that depose Viceroy Cisneros at Buenos Aires.The revolution spreads all over the Viceroyalty, except for Paraguay (which declares itself an independent nation in 1811) and Upper Peru (which remains controlled by royalist troops from Lima, and is eventually re-incorporated into the Viceroyalty of Peru).

Meanwhile, the Governor of Montevideo Francisco Javier de Elío, appointed as a new Viceroy by the Cortes of Cádiz in 1811, declares the Buenos Aires Junta seditious.

However, after being defeated at Las Piedras he is only left in control of Colonia del Sacramento and Montevideo, so he returns to Spain on November 18 and resigns as Viceroy on January 1812.

By 1814, as the patriots enter Montevideo, following a years-long siege, the Viceroyalty effectively ceases to exist.