The use of reinforced concrete in Greece coincides with the intensive building activity in the country in the twentieth century, and its “secrets” are known to thousands of engineers as well as to craftsmen. Particularly in Greece of the early twenty-first century the use of reinforced concrete is considered the simplest way to erect a building, not to mention that the use of metal for the construction of big technical works (bridges, large roofs, stadiums), although much more difficult in application, is regarded as a matter of course. These two building materials, iron, from the end of the nineteenth century, and reinforced concrete, from the beginning of the twentieth have penetrated the building sector superseding stone and wood, the age long traditional building materials. Iron as building element was used for the construction of factories and Neoclassical mansions around the end of the 1870’s, while the technique of iron construction was continuously developing until about 1905, and can boast grand and bold applications mainly in industrial, harbor and rail works. Reinforced concrete was introduced in Greece in 1901, was essentially established in the 1920’s and was extensively used from then on until the World War II for the erection of hundreds of factories, hospitals, schools and urban blocks of flats of modernistic architecture. Some of the avant-garde reinforce concrete buildings had no followers as opposed t the urban blocks of flats of the 1930’s that became influential models. The basic typology of their architecture and particularly the in situ method of construction have remained unchanged since then. Meanwhile, reinforced concrete as building material transgressed the boundaries of specialized firms and came slowly at the disposal of every minor contractor or craftsman.