The Glass Key is a crime novel by Dashiell Hammett, published by Knopf in 1931 (immediately following the publication of the successful The Maltese Falcon). The novel's central crime is the murder of one Taylor Henry, who is found dead in China Street nearby the Log Cabin Club—a gambling establishment where a group of gamblers and mob boss Paul Madvig do business. Taylor Henry is the son of a senator to whom the powerful Madvig gives his support in the interest of marrying his daughter, Janet.

Madvig is friends with the primary protagonist, Ned Beaumont, a gambler and small-time criminal. It is Beaumont who finds Taylor Henry's body in the street. After he finds the body, he approaches Madvig before going to the police. Madvig gives him permission to do so. The discovery of the murder coincides with Ned having won a lot of money on a horse race; however, when he goes to collect the money, the bookie, Bernie Despain, is missing. Keen on getting his money, Beaumont follows Despain and plants Taylor's hat, threatening to incriminate him and thus extorting his money.

It is suggested that Madvig and Beaumont are unsavory characters for the way they treat a stammering fellow gambler, Walter Ivans, to whom Madvig owes money. This Walter Ivans later goes to a rival mob boss, Shad O'Rory, who kills a witness to Ivans's brother's crime, thus setting in motion a heightened antagonism between O'Rory and Madvig. O'Rory tortures Beaumont, leading the latter to a hospital. In the hospital, his discussions with Madvig's daughter, Opal (who herself had been romantically, but secretly, involved with the senator's murdered son), as well as with Madvig's love interest, Janet, lead him to believe that Madvig is innocent, despite Opal's insistence that he is guilty.

Madvig confesses that he had a fight with Taylor Henry on the evening of the murder, and that he killed Taylor with the latter's own cane. Beaumont's further investigations lead him to discover that the senator himself intervened to finish his son off, angered by his own son's audacity to fight with Madvig, who backed the senator for re-election. Beaumont calls the police, and Madvig is exonerated, but the two are no longer friends.

Janet (the senator's daughter and Madvig's former love interest) plans to begin living with Beaumont in New York. The title is taken from a dream that Janet had in which she and Beaumont enter a house using a glass key.