Portuguese maritime explorations resulted in numerous territories and maritime routes recorded by the Portuguese on journeys during the 15th and 16th centuries. Portuguese sailors were at the vanguard of European exploration, chronicling and mapping the coasts of Africa and Asia, then known as the East Indies, Canada and Brazil (the West Indies), in what became known as the Age of Discovery.

Methodical expeditions started in 1419 along the coast of West Africa under the sponsorship of prince Henry the Navigator, whence Bartolomeu Dias reached the Cape of Good Hope and entered the Indian Ocean in 1488. Ten years later, in 1498, Vasco da Gama led the first fleet around Africa to the Indian subcontinent, arriving in Calicut and starting a maritime route from Portugal to India. Portuguese explorations then proceeded to southeast Asia, where they reached Japan in 1542, forty-four years after their first arrival in India. In 1500, the Portuguese nobleman Pedro Álvares Cabral became the first European to discover Brazil.

In 1297, King Dinis of Portugal took personal interest in the development of exports and organized that of surplus foreign production to European countries. On May 10, 1293, he instituted a maritime insurance fund for Portuguese traders living in the County of Flanders, which were to pay certain sums according to tonnage, accrued to them when necessary. Wine and dried fruits from Algarve were sold in Flanders and England, salt from Setúbal and Aveiro was a profitable export to northern Europe, and leather and kermes, a scarlet dye, were also exported. Portugal imported armor and munitions, fine clothes, and several manufactured products from Flanders and Italy.

In 1317, King Dinis made an agreement with Genoese merchant sailor Manuel Pessanha (Pessagno), appointing him first Admiral with trade privileges with his homeland in return for twenty warships and crews, with the goal of defending the country against Muslim pirate raids, thus laying the basis for the Portuguese Navy and establishment of a Genoese merchant community in Portugal. Forced to reduce their activities in the Black Sea, the Republic of Genoa had turned to North Africa for trade in wheat and olive oil and a search for gold – navigating also into the ports of Bruges (Flanders) and England. Genoese and Florentine communities were established in Portugal, which profited from the enterprise and financial experience of these rivals of the Republic of Venice.^{[citation needed]}

In the second half of the fourteenth century outbreaks of bubonic plague led to severe depopulation: the economy was extremely localized in a few towns, and migration from the country led to the abandonment of agricultural land and an increase in rural unemployment. Only the sea offered opportunities, with most people settling in fishing and trading areas along the coast. Between 1325 and 1357 Afonso IV of Portugal granted public funding to raise a proper commercial fleet and ordered the first maritime explorations, with the help of Genoese, under command of admiral Manuel Pessanha. In 1341 the Canary Islands, already known to Genoese seafarers, were officially rediscovered under the patronage of the Portuguese king, but in 1344 Castile disputed ownership of them, further propelling the Portuguese naval efforts. The first victims of slave raids by Portuguese and Spanish were the Guanches of the Canary Islands, a people of Berber origin, who put up fierce resistance but were reduced to near extinction by pillaging and enslavement.

In 1415, the Portuguese occupied the North African city of Ceuta to gain a foothold in Morocco and control shipping through the Strait of Gibraltar. They also hoped to extend Christianity and provide an outlet for Portuguese nobles looking to gain riches and honor in war. Among the participants of the action was the young Prince Henry the Navigator. Appointed governor of the Order of Christ in 1420, while personally holding profitable monopolies on resources in Algarve, he took the lead role in encouraging Portuguese maritime exploration until his death in 1460. He invested in sponsoring voyages down the coast of Mauritania, gathering a group of merchants, shipowners, and other stakeholders interested in new opportunities for maritime trade. Later his brother Prince Pedro granted him a royal monopoly of all profits from trading within the areas discovered.

In 1418, two of Henry's captains, João Gonçalves Zarco and Tristão Vaz Teixeira were driven by a storm to Porto Santo an uninhabited island off the coast of Africa which may have been known to Europeans since the 14th century. In 1419 Zarco and Teixeira made a landfall on Madeira. They returned with Bartolomeu Perestrelo, and Portuguese settlement of the islands began. There, wheat and later sugarcane were cultivated, as in Algarve, by the Genoese, becoming profitable activities. This helped both them and Prince Henry become wealthier.

A Portuguese attempt to capture Grand Canary, one of the nearby Canary Islands, which had been partially settled by Spaniards in 1402 was unsuccessful and met with protestations from Castile. Although the exact details are uncertain, cartographic evidence suggests the Azores were probably discovered in 1427 by Portuguese ships sailing under Henry's direction, and settled in 1432, suggesting that the Portuguese were able to navigate at least 745 miles (1,200 km) from the Portuguese coast.