Department of Architecture deals with the study of architecture, architects and architecturaldevelopment in the 20th and 21st centuries on the territory of countries which have been Slovenian territory in the history and where Slovenian architects have been working. The archives and documents of contemporary Slovenian architecture comprises the plans, drawings, sketches, designs, letters, photos, movies and other material from the legacies of architects. Among other things, these legacies comprise books, files, folders, projects, journals and newspapers, brochures and other items. At the end of 2010, the collection consisted of 80 archives of Slovenian architects, which means approximately 66,000 units of material. The material is continually being updated with new items in the form of gifts, redemptions and copying documents from private archives. Due to the fact that the founding of the Architectural Museum of Ljubljana in 1972 was related to the redemption of Plečnik's legacy, the museum has devoted a lot of its work to Plečnik.

The architectural depots at Museum of Architecture and Design store various documents on the work of almost all prominent Slovenian architects: Plečnik`s contemporary Ivan Vurnik and Behrens' students Ivo Spinčić, Jože Mesar and Feri Novak. Moreover, also extensive archives of architects Dušan Grabrijan, Gizela Šuklje, Stanko Rohrman, Danilo Fürst, Ivo Medved, Max Strenar, Boris Kobe and Plečnik's master builder Anton Suhadolc. Archives of Ivan Jager, Miha Osolin, Domicijan Serajnik, Jaroslav Černigoj, Vinko Glanz, France Tomažič, Ciril Tavčar, Vladimira Bratuž and others are also of significant importance.

The collection includes all legacies of Plečnik's students, who in 1930s also gathered additional knowledge in Paris, on Rue de Sèvres 35, from the famous architect Le Corbusier. Miscellaneous material, which is still at the stage of being recorded and studied, is connected to architects Miroslav Oražem, Milan Sever, Hrvoje Brnčič, Marjan Tepina, Edvard Ravnikar (a legacy from the Faculty of Architecture in Ljubljana), Jovan Krunić and Marko Zupančič. In the last few years, Museum of Architecture and Design has gained most material from former students of Edvard Ravnikar: Vladimir Braco Mušič, Anton Pibernik, Miloš Lapajne, Majda Dobravc Lajovic, Janez Lajovic, Stanko Kristl, Katarina Bebler, Marija Vovk, Nevenka Sterlekar, Branka Tancig Novak and others. Special attention is dedicated to material about the B Direction, an academic program at the Faculty of Architecture in the school year 1960/61. In addition, there is a vast archive of designer Niko Kralj and also a lot of very interesting documentation (donated by Zorka Šubic Ciani, Mladen Šubic and Janez Koželj) about architect Vladimir Šubic, who designed Ljubljana's Skyscraper.

Department of Architecture also documents the development of architecture in Slovenia, from its beginnings to the modern period. The collection consists mainly of older and newer analogue and digital photos of architectural monuments in Slovenia, from prehistory to modern times. The collection includes also a series of wooden models of older architectural monuments, which were created particularly in connection with exhibitions of older architecture, and originals and copies of older and newer drawings and plans of individual architectural monuments.