Which Stendhal's novel is considered to be his most important work?

"The Red and the Black" is a historical psychological novel in two volumes by Stendhal, published in 1830. It chronicles the attempts of a provincial young man to rise socially beyond his modest upbringing through a combination of talent, hard work, deception, and hypocrisy. He ultimately allows his passions to betray him.

"The Red and the Black" was a novel ahead of its time, that it was a novel for readers in the 20th century. In Stendhal's time, prose novels included dialogue and omniscient narrator descriptions; Stendhal's great contribution to literary technique was the describing of the psychologies (feelings, thoughts, and interior monologues) of the characters. As a result, he is considered the creator of the psychological novel.