Thomas Mann did not intend to write an epic against contemporary aristocratic society and its conventions. On the contrary, Mann often sympathizes with their Protestant ethics. Mann criticizes with irony and detachment. When Die protestantische Ethik und der 'Geist' des Kapitalismus (1905, The Protestant Ethic and the Spirit of Capitalism) by Max Weber was published, Thomas Mann himself recognised the affinities with his own novel. The same happened with Religion and the Rise of Capitalism (1926) by R.H. Tawney. (See Hugh Ridley's Thomas Mann: Buddenbrooks – Cambridge, 1987.)
Before writing the novel, Mann conducted extensive research in order to depict with immaculate detail the conditions of the times and even the mundane aspects of the lives of his characters. In particular, his cousin Marty provided him with substantial information on the economics of Lübeck, including grain prices and the city's economic decline. The author carried out financial analysis to present the economic information depicted in the book accurately.
Accurate information through extensive research was a general topic in Thomas Mann's other novels. Some characters in the book speak in the Low German of northern Germany.
In the conversations appearing in the early parts of the book, many of the characters switch back and forth between German and French, and are seen to be effectively bilingual. The French appears in the original within Mann's German text, similar to the practice of Tolstoy in War and Peace. The bilingual characters are of the older generation, who were already adults during the Napoleonic Wars; in later parts of the book, with the focus shifting to the family's younger generation against the background of Germany moving towards unification and assertion of its new role as a major European power, the use of French by the characters visibly diminishes.
All occurrences in the lives of the characters are seen by the narrator and the family members in relation to the family trade business: the sense of duty and destiny accompanying it as well as the economic consequences that events bring. Through births, marriages, and deaths, the business becomes almost a fetish or a religion, especially for some characters, notably Thomas and his sister Tony. The treatment of the female main character Tony Buddenbrook in the novel resembles the 19th-century Realists (Flaubert's Madame Bovary and Leo Tolstoy's Anna Karenina), but from a more ironic and less tragic point of view.
The influence of Buddenbrooks on later novels of the 20th century is probably less than Mann's other novels. Nonetheless, William Faulkner said of the novel that it was for him "the greatest novel of the century" and kept an edition of Buddenbrooks in his home library bearing Mann's own signature.
Mann's emotional description of the Frau Consul's death has been noted as a significant literary treatment of death and the subject's self-awareness of the death process.