Resum

This article sets out to establish a pattern in the progress of library architecture during the twentieth and twenty-first centuries by examining the structural transformations that library buildings have undergone to adjust to our changing social and cultural reality and to meet the more general dictates of different periods and moments. It argues that, historically, these transformations can be grouped in five, separate periods and it focuses for each period on the main architectural features of a building or selection of buildings from around the world. Finally, the article also supports this division in five periods with a series of citations of external sources and a proposal. The result is a chronological and historical study that helps to put the fifth (ongoing) period in clearer context.