The Spanish Navy, officially the Armada, is the maritime branch of the Spanish Armed Forces and one of the oldest active naval forces in the world. The Spanish Navy was responsible for a number of major historic achievements in navigation, the most famous being the discovery of North America and the first global circumnavigation. For several centuries, it played a crucial logistical role in the expansion and consolidation of the Spanish Empire, and defended a vast trade network across the Atlantic Ocean between the Americas and Europe, and the Manila Galleon across the Pacific Ocean between the Philippines and the Americas.

The Spanish Navy was one of the most powerful maritime forces in the world from the late 15th century to mid-18th century. In the early 19th century, with the loss of most of its empire, the Spanish navy transitioned to a smaller fleet but it still maintained a significant shipbuilding capability and produced the first fully capable military submarine. In this time, the Spanish navy also contributed to the development of the destroyer class of warship and achieved the first global circumnavigation by an ironclad vessel.

The main bases of the Spanish Navy are at Rota, Ferrol, San Fernando and Cartagena.

The roots of the modern Spanish Navy date back to before the unification of Spain. By the late Middle Ages, the two principal kingdoms that would later combine to form Spain, Aragon and Castile, had developed powerful fleets. Aragon possessed the third largest navy in the late medieval Mediterranean, although its capabilities were exceeded by those of Venice and (until overtaken in the 15th century by those of Aragon) Genoa. In the 14th and 15th centuries, these naval capabilities enabled Aragon to assemble the largest collection of territories of any European power in the Mediterranean, encompassing the Balearics, Sardinia, Sicily, southern Italy and, briefly, the Duchy of Athens.

Castile meanwhile used its naval capacities to conduct its Reconquista operations against the Moors, capturing Cádiz in 1232 and also to help the French Crown against England in the Hundred Years' War. In 1375, a Castilian fleet destroyed a large English fleet at Bourgneuf, and Castilian ships raided the English coast. As Castile developed long-lasting trade relationships with towns in the Low Countries of the Netherlands and Flanders, the English Channel virtually became the "Spanish Channel." In 1402, a Castilian expedition led by Juan de Bethencourt conquered the Canary Islands for Henry III of Castile. In 1419, the Castilians defeated the German Hanseatic League at sea and excluded them from the Bay of Biscay.

In the 15th century, Castile entered into a race of exploration with Portugal, the country that inaugurated the European Age of Discovery. In 1492, two caravels and a carrack, commanded by Christopher Columbus, arrived in America, on an expedition that sought a westward oceanic passage across the Atlantic, to the Far East. This began the era of trans-oceanic trade routes, pioneered by the Spanish in the seas to the west of Europe and the Portuguese to the east.

Following the discovery of America and the settlement of certain Caribbean islands, such as Cuba, Spanish conquistadors Hernán Cortés and Francisco Pizarro were carried by the Spanish Navy to the mainland, where they conquered Mexico and Peru respectively. The navy also carried explorers to the North American mainland, including Juan Ponce de León and Álvarez de Pineda, who discovered Florida (1519) and Texas (1521) respectively. In 1519, Spain sent out the first expedition of world circumnavigation in history, which was put in the charge of the Portuguese Commander Ferdinand Magellan. Following the death of Magellan in the Philippines, the expedition was completed under the command of Juan Sebastián Elcano in 1522. In 1565, a follow-on expedition by Miguel López de Legazpi was carried by the navy from New Spain (Mexico) to the Philippines via Guam to establish the Spanish East Indies, a base for trade with the Orient. For two and a half centuries, the Manila galleons operated across the Pacific linking Manila and Acapulco. Until the early 17th century, the Pacific Ocean was dominated by the Spanish Navy. Aside from the Marianas and Caroline Islands, several naval expeditions also discovered the Tuvalu archipelago, the Marquesas, the Solomon Islands and New Guinea in the South Pacific. In the quest for Terra Australis, Spanish explorers in the 17th century also discovered the Pitcairn and Vanuatu archipelagos. Most significantly, from 1565 Spanish fleets explored and colonised the Philippine archipelago, the Spanish East Indies.

After the unification of its kingdoms under the House of Habsburg, Spain maintained two largely separate fleets, one consisting chiefly of galleys for use in the Mediterranean and the other of sailing ships for the Atlantic, successors to the Aragonese and Castilian navies respectively. This arrangement continued until superseded by the decline of galley warfare during the 17th century. The completion of the Reconquista with the conquest of the Kingdom of Granada in 1492 had been followed by naval expansion in the Mediterranean, where Spain seized control of almost every significant port along the coast of North Africa west of Cyrenaica, notably Melilla (captured 1497), Mers El Kébir (1505), Oran (1509), Algiers (1510) and Tripoli (1510), which marked the furthest point of this advance. However, the hinterlands of these ports remained under the control of their Muslim and Berber inhabitants, and the expanding naval power of the Ottoman Empire brought about a major Islamic counter-offensive, which embroiled Spain in decades of intense warfare for control of the Mediterranean. The war saw cooperation with the Republic of Genoa under the leadership of Andrea Doria, while the Ottomans found an ally in France. In its course, the Spanish under Álvaro de Bazán the Elder would defeat the French in the first large modern battle in the Atlantic in Muros Bay.