Art Nouveau is the style of art of the late 19th and early 20th century. It introduced the system of contemporary styles in architecture. The creative principle of Art Nouveau was an artistically expressive interpretation of the utilitarian elements of the building i.e. functional planning, structural elements, building materials etc Inherent to Art Nouveau are several different formal artistic trends, such as Eclectically decorative, rationalistic, among them predominantly so called Perpendicular Art Nouveau, and National romanticism. The essence of style is not in ornamental décor, however a number of Art Nouveau buildings bear ornamentation, peculiar to only this style.

Development of Art Nouveau in Riga coincided with an unprecedented boom of the city growth. The number of inhabitants rapidly increased. Several years witnessed the construction of more than a hundred multi-storey masonry buildings. At the beginning of the 20th century Riga centre acquired its present cityscape. By 1904 the eclectic style of the second half of the 19th century almost completely disappeared. Buildings of Art Nouveau represent nearly 40% of the whole inventory of the city centre.

Local architects developed a very prolific activity. About 250 multi-storey buildings were constructed after projects by K. Pēkšēns, J. Alksnis is responsible for 140 such structures. The contribution of other architects is respectively as follows: O. Bārs, R. Donbergs, E. Laube – about 80 buildings, A. Vanags – 70, P. Mandelštams and E. Pole – 40, B. Bīlenšteins – 30, M. Nukša – 20. Most of them are graduates of the Riga Polytechnical Institute.
Inherit feature to this stylistic trend is an exaggeration of ornamental trimmings, which lack direct link with the architecture of the building and quite often are arranged evenly rhythmical compositions typical of Eclecticism of the 19th century. Thus it is difficult from afar to distinguish these buildings from those of the previous style. Only the decorative motifs – curvilinear, stressed lines, geometric figures or stylized floral ornaments, masks, elongated proportions etc. – are innovative for the period.
Examples of eclectically decorative trend appeared at the beginning of Art Nouveau period, and Riga has only a few of them. The characteristic works are those of civil engineer M. Eisenstein in Alberta Street and its vicinity, as well as several buildings by Heinrich Scheel, Friedrich Scheffel, Rudolph Zirkvitz, Jānis Alksnis and some other architects.

One of the most characteristic formal trends of Art Nouveau architecture of Riga. It became popular after 1906, when romantically stylized motifs in the façades of the buildings step-by-step disappeared. This was a substyle that accentuated vertical composition by strongly articulated several-storey high bay windows, profiled upright mouldings frequently breaking window bays and ornamental reliefs on the spandrels. This ornamentation was completely integrated into the basic architectural form and at the same time highlighted its vertical composition. Buildings in this vein make up more than one third of Riga's diverse Art Nouveau heritage. There are areas in Riga where this trend completely dominates the cityscape (in Brīvības iela, Ģertrūdes iela, Aleksandrqa Čaka iela and other streets). ”Perpendicular Art Nouveau” is widely represented in the creations by Jānis Alksnis, Eižens Laube, Bernhard Bielenstein, Oskars Bārs, Paul Mandelstamm and other architects.
Reflects the attempt of Riga architects to create specific Latvian architecture. This trend of Art Nouveau flourished between 1905 and 1911. It was inspired by applied folk art and vernacular architecture. Latvian architects insisted on using of natural building materials. Buildings in the National romanticism vein are characterized by a solid appearance, a monumental dignity, steep roofs, window apertures with a tapered upper part, ornamentation utilizing ethnographic motifs presented in a rather restrained manner and sometimes reproduced according to the principles of the Art Nouveau aesthetic, that is, with rounded, sinuous patterns. Every third or fourth Art Nouveau building in Riga can be categorized as belonging to National Romanticism.
Metal lintels, cantilevers and other structural elements are often used as means of artistic expression. The most outstanding masters of National romanticism are Eižens Laube, Konstantīns Pēkšēns, Aleksandrs Vanags and Augusts Malvess.
Some traits of this stylistic trend can be seen also in several works of local Baltic Germans.