Portuguese architecture refers to both the architecture of Portugal's modern-day territory in Continental Portugal, the Azores and Madeira, as well as the architectural heritage/patrimony of Portuguese architects and styles throughout the world, particularly in countries formerly part of the Portuguese Empire.

Like all aspects of Portuguese culture, Portuguese architecture reflects the artistic influences of the various cultures that have either inhabited Portugal or come in contact with the Portuguese people throughout the history of Portugal, including the Gallaecians, Lusitanians, Celtiberians, Romans, Suebi, Visigoths, Moors, Goans, Macanese, Kristang people, and many more. Because of the history of the Portuguese Empire, several countries across the world are home to sizable heritages of Portuguese colonial architecture, notably Brazil and Uruguay in the Americas, Angola, Cabo Verde, São Tomé and Príncipe, Benin, Ghana, Morocco, Guinea Bissau, Zimbabwe, and Mozambique in Africa, and China, India, Indonesia, Malaysia, and Timor Leste in Asia.

Various artistic styles or movements have dominated Portuguese architecture throughout the ages, including Romanesque, Gothic, Manueline, Portuguese Renaissance, Portuguese Baroque, Rococo, Pombaline, Neo-Manueline, Soft Portuguese style, and contemporary architecture. Notable Portuguese architects of the past have included Diogo de Arruda (15–16th c.), João Antunes (17th c.), Eugénio dos Santos and Carlos Mardel (18th c.), José Luis Monteiro (19th c.), Raul Lino, Cassiano Branco and Fernando Távora (20th c.). Famous living architects include Gonçalo Byrne, Eduardo Souto de Moura (Pritzker winner), António Maria Braga, João Carrilho da Graça and Álvaro Siza Vieira (Priktzer winner).

The earliest examples of architectural activity in Portugal date from the Neolithic and consist of structures associated with Megalith culture. The Portuguese hinterland is dotted with a large number of dolmens (called antas or dólmens), tumuli (mamoas) and menhirs. The Alentejo region is particularly rich in megalithic monuments, like the notable Anta Grande do Zambujeiro, located near Évora. Standing stones can be found isolated or forming circular arrays (stone circles or cromlechs). The Almendres Cromlech, also located near Évora, is the largest of the Iberian Peninsula, containing nearly 100 menhirs arranged in two elliptical arrays on an east–west orientation.

Celtic pre-historic fortified villages dating from the Chalcolithic are found along the Tagus river like that of Vila Nova de São Pedro, near Cartaxo, and the Castro of Zambujal, near Torres Vedras. These sites were occupied in the period around 2500–1700 BC and were surrounded by stone walls and towers, a sign of the conflicts of the time.

Starting around the 6th century BC, Northern Portugal, as well as neighbouring Galicia, saw the development of the Celtic Castro culture (cultura castreja). This region was dotted with hillfort villages (called citânias or cividades) that for the most part continued to exist under Roman domination, when the area became incorporated into the province of Gallaecia. Notable archaeological castro sites are the Citânia de Sanfins, near Paços de Ferreira, Citânia de Briteiros and Citânia de Sabroso [pt], near Guimarães, and the Cividade de Terroso, near Póvoa do Varzim. For defensive reasons, these hillforts were built over elevated terrain and were surrounded by rings of stone walls (Terroso had three wall rings). The houses inside the castros are about 3.5 to 5 meters long, mostly circular with some rectangular, stone-made and with thatch roofs which rested on a wood column in the centre of the building. Their streets are somewhat regular, suggesting some form of central organization. Baths were built in some of them, like in Briteiros and Sanfins.

Architecture developed significantly in the 2nd century BC with the arrival of the Romans, who called the Iberian Peninsula Hispania. Conquered settlements and villages were often modernised following Roman models, with the building of a forum, streets, theatres, temples, baths, aqueducts and other public buildings. An efficient array of roads and bridges was built to link the cities and other settlements.

Braga (Bracara Augusta) was the capital of the Gallaecia province and still has vestiges of public baths, a public fountain (called Idol's Fountain) and a theatre. Évora boasts a well-preserved Roman temple, probably dedicated to the cult of Emperor Augustus. A Roman bridge crosses the Tâmega River by the city of Chaves (Aquae Flaviae). Lisbon (Olissipo) has the remains of a theatre in the Alfama neighbourhood.