The Heart of the Matter (1948) is a novel by English author Graham Greene. The book details a life-changing moral crisis for Henry Scobie. Greene, a former British intelligence officer in Freetown, British Sierra Leone, drew on his experience there. Although Freetown is not mentioned in the novel, Greene confirms the location in his 1980 memoir, Ways of Escape.

The Heart of the Matter was enormously popular, selling more than 300,000 copies in the United Kingdom upon its release. It won the 1948 James Tait Black Memorial Prize for fiction. In 1998, the Modern Library ranked The Heart of the Matter 40th on its list of the 100 best English-language novels of the 20th century. In 2005, the novel was chosen by Time magazine as one of the one hundred best English-language novels from 1923 to the present. In 2012, it was shortlisted for the Best of the James Tait Black.

The book's title appears halfway through the novel: "If one knew, he wondered, the facts, would one have to feel pity even for the planets? If one reached what they called the heart of the matter?"

Major Scobie lives in a colony on the west coast of Africa during World War II, and is responsible for local security during wartime. His wife Louise, an unhappy, solitary woman who loves literature and poetry, cannot make friends. Scobie feels responsible for her misery, but does not love her. Their only child, Catherine, died in England several years before. Louise is a devout Catholic. Scobie, a convert, is also devout.

Throughout the novel the oppressive nature of the climate is a major backdrop. The heat and humidity act as weakening factors.

Scobie is passed over for promotion to commissioner, which upsets Louise both for her personal ambition and her hope that the local British community will begin to accept her. Louise asks Scobie if she can go to live in South Africa to escape a life she hates.

At the same time, a new inspector, named Wilson, arrives in the town. He is priggish and socially inept, and hides his passion for poetry for fear of ostracism by his colleagues. He and Louise strike up a friendship, which Wilson mistakes for love. Wilson rooms with another colleague named Harris, who has created a sport for himself of killing the cockroaches that appear in his room each night. He invites Wilson to join him, but in the first match, they end up quarrelling over the rules of engagement.

One of Scobie's duties is to lead the inspections of local passenger ships, particularly looking for smuggled diamonds, a needle-in-a-haystack problem that never yields results. A Portuguese ship, the Esperança (the Portuguese word for 'hope'), comes into port, and a disgruntled steward reveals the location of a letter hidden in the captain's quarters. Scobie finds it, and because it is addressed to someone in Germany, he confiscates it, as it might contain secret codes and clandestine information. The captain says it is a letter to his daughter and begs Scobie to forget the incident, offering him a bribe of one hundred pounds when he learns that they share the Catholic faith. Scobie declines the bribe and takes the letter, but having opened and read it—contrary to regulations—and finding it innocuous, he decides not to submit it to higher authorities, and burns it.