Monsters of Men is a young adult science fiction novel by Patrick Ness, published by Walker Books in May 2010. It is the third book of the Chaos Walking trilogy inaugurated two years earlier by The Knife of Never Letting Go. Walker's U.S. division Candlewick Press published hardcover and audiobook editions within the calendar year.

Ness won the annual Carnegie Medal from CILIP, recognising the year's best new book for children or young adults published in the U.K.

The title is taken from previous dialogue in the series; "War makes monsters of men" is said in Knife, which both Todd and Viola later quote.

An army of Spackle marches on New Prentisstown from one direction, and the forces of The Answer from the other. Mayor Prentiss has been freed by Todd to help defend the city, while Viola attempts to warn incoming settlers.

Prentiss' army and the Spackle's engage in combat. Viola and Mistress Coyle confer with Bradley and Simone, the scout ship pilots; Coyle wants to use the ship's missiles to destroy Prentiss. Prentiss' army pushes the Spackle army back into the forest. 1017, now named "The Return", has made his way to the Spackle camp. He is the only surviving slave and seeks revenge on Todd and the settlers.

The Spackle dam off the river to block the water supply and attack Prentiss' camp. Coyle attempts to manipulate Viola to use the scout ship, and when Todd is in danger, she launches a missile that kills most Spackle warriors. The Return argues with The Sky, the leader of the Spackle, demanding more attacks. The Sky refuses but reveals a captured, hibernating Ben, Todd's adoptive father. The Sky promises Ben to The Return if the two armies reach peace. The Spackle begin attacking the town at random. During a raid, Todd knocks Prentiss unconscious and takes over. Prentiss praises him for having such ability.

Prentiss' army without water, and The Answer without food, are forced into a peace talk. The two groups work together – Prentiss lures Spackle and The Answer provides bombs. Angry that Prentiss undermines her, Coyle sends a bomb into the Spackle stronghold. The Spackle respond with a message to send two people to meet the next morning.

Viola and Bradley are sent to negotiate with the Spackle. The Return attempts to murder Viola in revenge, but stops when he sees the ID band on her arm, sympathising. Although the peace talks are successful, the Spackle launch a surprise attack on Prentiss and Todd the next day. Prentiss, planning ahead, had already set up his artillery and soldiers. After killing the attacking Spackle, The Sky surrenders. The Return goes to kill Ben, angered by both the surrender and his inability to kill Viola. The Sky meets him there, and watches as The Return fails to murder Ben. Ben wakes.

During a speech, Mistress Coyle reveals a suicide bomb, intent on killing Prentiss. Todd inadvertently saves him. Later, Ben and The Return arrive. Todd, overwhelmed by happiness, rejoins Ben and leaves Prentiss' side. The settlers plan to settle peace, leaving Todd and Prentiss alone. Angered by Todd's decision to leave his side, Prentiss captures him and steals the scout ship. Prentiss launches flammable fuel at the forest, killing many Spackle, including The Sky who passes leadership to The Return.