Modern architecture appeared in Lebanon with the appearance of new building techniques and materials, which revolutionized the conception of building, and namely with the introduction of concrete in the1920's, which was first imported, then locally produced, after 1930. The course of modernism in Lebanon thus appears to gradually take off in the late 1930's, with some delay compared to European modernism, with the adaptation of new technologies and spatial concepts in design.
The period of its golden age, where many constructions that exhibit a mature modernist spirit begin to appear was during the 1950's, after Independence, when the new nation and its new capital, began to capitalize on the new social, political and economic dynamics which turned Beirut into the avant-garde capital of the Arab world. This golden age would continue in the 1960's with a new generation of local architects and engineers who further developed and consolidated the appropriation of modern architecture.
This drive was to slowly lose its momentum with the unfortunate unraveling of the civil war [1975-1991], and the arrival of new ideas and styles such as post-modernism in the 1980's. This period witnessed a mixture of formalistic tendencies, further compounded by the conscious desire to assert a regionalist identity after the end of the war, exemplified by the re-make of important landmarks of modernism, such as the Presidential Palace in Baabda and the Artisans House in Beirut, which were re-designed to take a more domesticated appearance.
The pioneers of this new movement in architecture were a select group of engineers and architects, among them:
Ilyas Murr (1884-1976) the first Lebanese engineer to graduate from the Massachusetts Institute of Technology in 1905. Among his projects figures the Roxy movie theater in 1932, in the center of Beirut, in an Art Deco style.
Mardiros Altounian (1889-1958) graduated from the Ecole des Beaux Arts in Paris in 1918. Besides his well known building for the Parliament (1931) and the Abed clock tower (1934) he designed in 1937 the Azounieh sanatorium in the Chouf region.
Farid Trad (1901-1969) graduated as an engineer from the Ecole Centrale des Arts et Manufactures in Paris in 1926. He designed a large number of villas in Beirut. His masterpiece, the Unesco palace designed in 1947 presents a monumental interpretation of modern architecture.
Antoine Tabet (1907-1964) graduated from the Ecole Superieure des Ingenieurs de Beyrouth [ESIB] in 1926. He worked in Paris under Auguste Perret, before designing in 1932 with three French architects [Jacques Poirrier, Georges Bordes and Andre Lotte] one of the emblematic works of early modernism in Beirut, the Hotel Saint Georges. Later on, Tabet designed the Almaza beer factory in 1934 and the Sagesse school in Achrafieh in 1937. In all of the above-mentioned projects, traces of the influence of Perret and his structuralist approach are clearly visible.
Antoine Tabet and Farid Trad are considered as the two pioneers of Modern Architecture in Lebanon.
The Fifties and the apogee of Modernism
In the fifties, modernism became assimilated within the architectural culture of Beirut and its suburbs, where in addition to a number of local architects and engineers applying the lessons of European modernism, a great number of foreign architects also brought with them their direct experience. The new generation of architects and engineers designed and executed a large number of projects that exhibited a mature understanding of modernism, adapted to the exigencies of the local climate and building traditions, and marked by a rational approach.
Among these architects:
Michel Ecochard (1905-1985) a French architect and urban planner who graduated from the Ecole des Beaux Arts in Paris. In 1943 he worked on the first master plan of Beirut. In 1955, he designed with another French architect Claude Lecoeur the College Protestant on Marie Curie Street. This educational facility shows a clear rational spirit in line with the early European avant-garde. Among the other projects by Ecochard, figures the Grand Lycee Franco-Libanais  and the Sacre-coeur hospital in Hazmieh , east of the capital.
Andre Leconte (1894-1990) French architect and holder of the "Prix de Rome" was commissioned by the Lebanese government to design the Beirut International Airport at Khalde [1948-1954]. Leconte designed two other major buildings in Beirut: the Lazarieh office building in the city center in 1953 and Rizk hospital built  in Achrafieh.
George Addor (1920-1982) Swiss architect graduated in 1948 from Zurich Polytechnic school, designed with his partner Dominique Julliard the Starco center in 1957, a project that recalls Mies van der Rohe's work. Later, the two partners designed the Central Bank building and the presidential palace  in Baabda.
George Rayes (1915-2002) Lebanese architect born in Alexandria, Egypt; studied at the Bartlett School and the Architecture Association. He designed with his partner Theo Kanaan (1910-1959) several projects that are considered as reference points in this golden period in which Lebanon enjoyed economic, social and cultural development. Together they realized an architecture that distinguishes itself by rationality and is characterized by a high degree of perfection in details. With Kanaan and Assem Salam, Rayes designed in 1955 the important landmark, the Pan American building in the center of the city.
Karl Schayer (1900-1971) was a Polish architect who graduated from the Polytechnic School of Lvov in 1920. In association with Fritz Gotthelf (1905-1980) a German interior designer and his Lebanese partners the architect Wassek Adib (1926-) and the engineer Bahij Makdissi (1916-1995) he set a team which became one of the major architectural firms. Among their many realizations are the AUB Alumni Club built in 1952, Dar al Sayad in 1954, and the Shell building . All these constructions express the arrival of an architecture influenced by new technological developments.
The Sixties and Seventies: Evolution and Consolidation
In the sixties and seventies a new generation of architects further developed new tendencies of modernisms from Brutalism to Structuralism and Latin American versions of Modernism. They applied the precepts of European functionalism and further developed the potentials of industrial and low cost materials like steel and reinforced concrete.
Among them, figure some of the assistants of Michel Ecochard, as Khalil Khoury and his brother Georges Khoury, as well as Gregoire Serof. Other important architects to emerge during this period are Raoul Verney who left a number of important landmarks in modern architecture, and Jacques Liger-Belair who is well known for his synthesis of modernism with local vernacular traditions as well as for his research and proposals for the preservation of towns and regional architecture.
In the sixties the Lebanese government and other private institutions also launched many architectural competitions. This gave an opportunity to many young architects to appear on the local scene, among them Pierre El Khoury, Pierre Neema, and Antoine Romanos to develop their practice.
The Brazilian architect Oscar Niemeyer also left his trace in Lebanon during this period, in a project commissioned by the government, the Tripoli International Fair which started in 1963 but remained unfinished by the beginning of the civil war in 1975.
Khalil Khoury (1929-) graduated in 1955 from the Academie Libanaise des Beaux Arts, his brother Georges Khoury (1933-) graduated in 1960 from the Ecole Speciale d'Architecture in Paris.
Gregoire Serof (1930-) also graduated in 1955 from the Academie Libanaise des Beaux Arts.
Raoul Verney (1930-) graduated in 1954 from the Ecole Superieure des Ingenieurs de Beyrouth. All four collaborated on a number of projects. At the end of the sixties they designed a major project, the College des Freres Mont La Salle at Ain Saade, a large educational facility composed of modular units of fair-faced concrete.
Among the other projects developed by the Khoury Brothers figures the later Manar Resort, a project designed in the 80's that follows clearly the lessons of Corbusier's Unite d'Habitation, but reduced at a smaller scale.
Among the many projects developed later by Raoul Verney figures prominently the Red Cross building in Jounieh, the Chapel in Faqra, and a number of private villas.
Joseph Philippe Karam (1923-1976) graduated in 1946 from the Ecole Superieure des Ingenieurs de Beyrouth. His short career is marked by the assimilation of Le Corbusier's syntax and his mastery of concrete in its various textures and treatments, as well as new techniques like colored glass paste. His production was representative of the optimism and development in the country between 1950 and 1960. Among his many projects figures the Teachers Institute in Jounieh.
Andre Wogensky (1916- ) French architect graduated in 1934 from the Ecole des Beaux Arts in Paris. Between 1935 and 1956 he was one of the principal assistants of Le Corbusier. With his partner, the Lebanese architect Maurice Hindieh he realized a major project, the Ministry of Defense built between 1962 and 1968 in the suburb of Yarze, east of Beirut and the Holiday Inn which was completed in 1975, at the beginning of the Civil War, and witnessed its earliest battles.
Assem Salam (1924) graduated in 1950 from the University of Cambridge.
Since launching his practice in 1952, Salam showed a deep interest in local interpretations of modernity. In 1965, he designed the Serail of Saîda, a modern edifice which shows the incorporation of traditional elements.
In 1968, he designed the Khachoggi Mosque, which shows affinities to Louis Kahn's geometric articulations, and is considered a landmark in contemporary Islamic architecture. Among his other realizations figures also the dormitories of Broumana High School 
Pierre El Khoury (1930) graduated in 1957 from the Ecole Nationale des Beaux Arts in Paris. Since starting his practice, he realized more than 200 projects. In 1959 he carried out his first project, his own house in the region of Yarze, a modern masterpiece in harmony with its wooded site. In 1966, El Khoury designed the British Bank in Beirut; a construction which inserts itself in a difficult site in the proximity of the nearby Saint Louis cathedral. Among his later major works figures the Cathedral of Harissa overlooking the bay of Jounieh.
Pierre Neema (1931-) graduated in 1958 from the Ecole Nationale des Beaux Arts in Paris, under the tutorship of Andre Leconte. With Jacques Aractingi (1932-) an engineer who graduated from ESIB in 1954, Jean-Noel Conan (1926-) a French architect who graduated in 1956 from the Ecole des Beaux Arts in Paris and Joseph Nassar (1931-) an engineer who graduated from ESIB in 1953, he realized in 1963 the Artisans House in Ain-Mreisseh in Beirut, a building that expresses a creative adaptation of modernism to local culture. In 1966, he won the competition for the headquarters of the Electricite du Liban in Beirut, a construction which is influenced by the Brazilian movement in modern architecture.
Jacques Liger-Belair (1933-) is a Belgian born architect, graduated in 1955 from the Ecole Superieure Saint Luc in Brussels, moved later to Beirut to set up his practice. Liger-Belair is motivated by two simultaneous approaches: the first is based on the assimilation of modernity and the use of concrete as a primary material, and the second is based on his interest in vernacular architecture. In 1967 Liger-Belair designed the chapel of the Monastery of Unity in Yarze, a project that shows his typical interest in the plastic potentials of fair-faced concrete. Among his numerous other projects figures also the School of Ain Najm.
Antoine Romanos (1944- ) graduated from the Ecole des Beaux Arts in Paris in 1969, where he studied under George Candilis, Alexi Josic and Shadrach Woods. Upon his return to Lebanon, he won the competition to design the SNA-Assurances headquarters in Beirut in 1970 a building that articulates the separation between serving and served spaces, between structure and infrastructure, within a rationally designed envelope of fair faced concrete. Among the other noteworthy examples of his work is Le The, a small multi-purpose structure in Beirut , with a modular system of partitions and exposed mechanical systems.