It portrays the downfall (already announced in the subtitle, Decline of a Family) of a wealthy mercantile family of Lübeck over four generations. The book is generally understood as a portrait of the German bourgeois society throughout several decades of the 19th century. The book displays Mann's characteristic detailed style, and it was this novel which won Mann the Nobel Prize in Literature in 1929, although according to Mann's wife this achievement would not have occurred without the publication of The Magic Mountain.

Thomas Mann started writing the book in October 1897, when he was twenty-two years old. The novel was completed three years later, in July 1900, and published in October 1901.

His objective was to write a novel on the conflicts between businessman and artist's worlds, presented as a family saga, continuing in the realist tradition of 19th century works such as Stendhal's Le Rouge et le noir (1830; The Red and the Black). More personally, he wanted to surpass the literary status already achieved by his eldest brother Heinrich Mann, who met relative success with the novel In einer Familie (1894, In a Family), and who was working at that time on another novel about German bourgeois society, Im Schlaraffenland (1900, In the Land of Cockaigne). It can be said that both of Thomas Mann's objectives were satisfied. The novel stands today as one of his most popular, especially in Germany, and is considered by many to be the novel that best captures the 19th century German bourgeois atmosphere.

Buddenbrooks is a transition novel, involving both the transition between the 19th century realistic style and 20th century symbolism; it is also a novel of personal transition for the author, starting his departure from 19th century influences to the more essayistic, symbolic and intertextual modern tone of his later works. That said, Buddenbrooks already presents in full style the perfection of narrative, the subtle irony of tone, and the complex and obsessively detailed character descriptions that characterize Mann's work.

Up to the time of writing Buddenbrooks, Mann had concentrated on smaller stories, almost all of which referred to his own difficult decision to live the life of an artist instead of continuing the commercial and otherwise bourgeois duties expected by his family. These stories had been already published under the title Der kleine Herr Friedemann (1898, Little Herr Friedmann). They treated spiritually and physically weak figures in an ambivalent way and demonstrated their fight against the moral and social constraints of bourgeois society. This same treatment reappears in the context of Buddenbrooks, and in different ways in some of Mann's later works.

The exploration of decadence in the novel can be attributed to the profound influence of Arthur Schopenhauer (see The World as Will and Representation also translated as The World as Will and Idea, 1829) on Thomas Mann during his youth. The three generations of the family depicted in the book experience a continuous economical, physical, and spiritual decline, with true happiness becoming increasingly unavailable to all the members of the family. The characters who sacrifice their lives for the sake of the family firm meet unfortunate ends, just as those who do not.

The city where the Buddenbrook family lives shares so many of its street names and other details with Mann's hometown of Lübeck that the identification is perfect, although Mann carefully avoids explicit pronunciation of the name throughout the whole novel. In spite of this fact, many German readers and critics attacked Mann for writing about the "dirty laundry" of his hometown and his own family. However, although this may be debated, it must be said that the fate of the Buddenbrooks bears no direct resemblance with the author's own family, nor with that of the 19th century German bourgeoisie in general, not even with the "money aristocracy", although merchandizing is a central topic.

The main period of time considered covers 1835 to 1877, and thus includes some of the most dramatic episodes of 19th-century German history: the Revolutions of 1848, the Austro-Prussian War, the North German Confederation, and the establishment of the German Empire). However, in agreement with the above-mentioned remarks these events play only a peripheral role and thus in this sense Buddenbrooks is also not a historical novel.

One of the most famous aspects of Thomas Mann's prose style can be seen in the use of leitmotifs. Derived from his admiration for the operas of Richard Wagner, in the case of Buddenbrooks an example can be found in the description of the color - blue and yellow, respectively - of the skin and the teeth of the characters. Each such description alludes to different states of health, personality and even the destiny of the characters. Rotting teeth are also a symbol of decay and decadence because it implies indulging in too many cavity causing foods. An example of this would be Tony's cup of hot chocolate at breakfast.

Many aspects of Thomas Mann's personality are represented in the two main male representatives of the third and the fourth generations of the fictional family: Thomas Buddenbrook and his son Hanno Buddenbrook. It should not be considered a coincidence that Mann shared the same first name with one of them. Thomas Buddenbrook reads a chapter of Schopenhauer's The World as Will and Idea, and the character of Hanno Buddenbrook escapes from real-life worries into the realm of music, Wagner's Tristan und Isolde in particular. (Wagner himself was of bourgeois descent and decided to dedicate himself to art.) In this sense both Buddenbrook persons symbolize the conflict lived by the author: the evasion of a productive bourgeois life to pursue an artistic one, though never turning his back on bourgeois ethics.