In 2075, underground colonies are scattered across the Moon (Luna), of which most inhabitants (called "Loonies") are criminals, political exiles, or descendants thereof. The total population is about three million, with men outnumbering women 2:1, so that polyandry is the norm. Although Earth's Protector of the Lunar Colonies (called the "Warden") holds power, in practice there is little intervention in the loose Lunar society.

HOLMES IV ("High-Optional, Logical, Multi-Evaluating Supervisor, Mark IV") is the Lunar Authority's master computer, having almost total control of Luna's machinery on the grounds that a single computer is cheaper than (though not as safe as) multiple independent systems.

The story is narrated by Manuel Garcia "Mannie" O'Kelly-Davis, a computer technician who discovers that HOLMES IV has achieved self-awareness and has developed a sense of humor. Mannie names it "Mike" after Mycroft Holmes, brother of Sherlock Holmes, and they become friends.

Major themesEdit


The first sixth of the book relates the discussions between the protagonists justifying and plotting the revolution; the next quarter describes the year-long revolution itself. The remainder of the book recounts events occurring in the months after the revolution in May 2076, and a week or so of events in October 2076 leading up to capitulation by Earth.

Politics and societyEdit

Professor Bernardo de La Paz describes himself as a Rational Anarchist; a name probably invented in the text itself. Rational Anarchists believe that the concepts of State, Society, and Government have no existence but for the "acts of self-responsible individuals", but concede that this is not a universal belief. The desire for anarchy is balanced by the logic that some form of government is needed, despite its flaws. Knowing this fact, a Rational Anarchist "tries to live perfectly in an imperfect world". When challenged by Wyoh, Professor de la Paz replies, "In terms of morals there is no such thing as a ‘state.’ Just men. Individuals. Each responsible for his own acts. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free, because I know that "I alone" am morally responsible for everything that I do."

Lunar society is portrayed as akin to that of the Old West, tempered by the closeness of death by exposure to vacuum and by the shortage of women. Although the sex ratio in 2075 is about 2 men to each woman, the result is a society where women have a great deal of power, and any man who offends or touches a woman uninvited is likely to be attacked and eliminated through the nearest airlock. Marriages tend to be polyandrous, including group marriages and Mannie's own line marriage. In discussion with a lady from Kentucky, Mannie implies that underground, three-dimensional Lunar estate is recorded in the name of the woman (or women) in a marriage. In a divorce, he implies, the separated man (or men) who contributed towards its cost would have money returned to him.

After decades during which anti-social individuals were selectively eliminated and the Authority exercised little real control, the Loonies live by the following Code: Pay your debts, collect what is owed to you, maintain your reputation and that of your family. As a result there is little theft, and disputes are settled privately or by informal Judges of good reputation. Failure to pay debts results in public shaming. Reputation is highly important in this society; with a bad reputation, a person may find others unwilling to buy from or sell to him. People are expected to pay back debts using all available funds.

Duels are permitted; but custom requires that anyone who kills another must pay debts and look after the deceased's family. Exceptions are allowed in the case of self-defense. Retaliatory killings do occur; but typically a consensus establishes which party was in the right, and there are no long-standing feuds. There is influence of the Vikings' mores on the Loonies, save that it is the society as a whole rather than the Althing which judges the actions of individuals.

Except where exchange involves the Authority, there is a generally-unregulated free market. The preferred currency is the dollar of the Bank of Hong Kong Luna, one hundred of which are exchangeable for a troy ounce of gold, a supply of which was shipped to Luna for this purpose, or more usefully for potable water or other commodities in published quantities. The Authority dollar circulates in dealings with the Authority; but this tends to lose ground over time against the Hong Kong Luna dollar.


Although the revolution succeeds in averting ecological disaster, the narrator decries the instincts of many of his fellow Loonies ("Rules, laws – always for [the] "other" fellow"). This theme is echoed elsewhere in Heinlein's works – that real liberty is to be found among the pioneer societies out along the advancing frontier, but the regimentation and legalism that follow bring restraints that chafe true individualists (an idea emphasized in the first and final page of the novel, and in the later book "The Cat Who Walks Through Walls").

Plot elementsEdit

As in "Stranger in a Strange Land", a band of social revolutionaries forms a secretive and hierarchical organization. In this respect, the revolution is more reminiscent of the Bolshevik October revolution than of the American, and this similarity is reinforced by the Russian flavor of the dialect, and the Russian place names such as Novy Leningrad.

Continuing Heinlein's speculation about unorthodox social and family structures, "The Moon Is a Harsh Mistress" introduces the idea of a line marriage. Mannie is part of a century-old line marriage, wherein new spouses are introduced by mutual consent at regular intervals so that the marriage never comes to an end. Divorce is rare, since divorcing a husband requires a unanimous decision on the part of all of his wives. Senior wives teach junior wives how to operate the family; granting financial security and ensuring that the children will never be orphaned. Children usually marry outside the line marriage, though this is not an ironclad rule. Mannie's youngest wife sports the last name 'Davis-Davis', showing she was both born and married into the line.

The social structure of the lunar society features complete racial integration, which becomes a vehicle for social commentary when Mannie, visiting the southeastern United States, is arrested for polygamy after he innocently shows a picture of his multiracial family to reporters, and learns that the "range of color in Davis family was what got [the] judge angry enough" to have him arrested. It is later revealed that this arrest was anticipated and provoked by his fellow conspirators to gain emotional support from Loonies when the arrest is announced.

The novel is notable stylistically for its use of an invented Lunar dialect consisting predominantly of standard English and Australian colloquial words but strongly influenced by Russian grammar, especially omission of article "the", which does not exist in most Slavic languages (cf. Nadsat slang from "A Clockwork Orange" by Anthony Burgess). This aspect of the Lunar dialect is explained by the fact that many of the deportees on Luna are Russian.

Earth politics and background historyEdit

The novel indicates that Earth had experienced a nuclear world war (the Wet Firecracker War) in the past century, although no significant traces of devastation are apparent at the time of the novel's setting.

Other changes include unification of the entire North American continent under a successor government to the United States, and political unification of South America, Europe, and Africa into mega-states. The Soviet Union seems to have lost the land east of the Urals to China into a rump state, and China has conquered all of East Asia, Southeast Asia, eastern Australia, and New Zealand (deporting unwanted people to Luna in the process). This Chinese aggrandizement is similar to that described in "Tunnel in the Sky" and, to a lesser extent, "Sixth Column". The militarily dominant nations seem to be North America and China. India is overcrowded but seems able to obtain much of the wheat shipments from Luna.

It is suggested that the Western nations, including North America, have become corrupt and authoritarian, while holding on to the vestiges of the pre-war democratic idealism in propaganda and popular culture. China is portrayed as plainly and unabashedly despotic, but no less technically advanced than the West. The Soviet Union seems to have relatively little influence, whereas the Lunar Authority itself is portrayed as corrupt. Most of Earth seems to have been split into several large nations, most joined together by the Federated Nations. They include the North American Directorate, Great China, Soviet Union, Pan Africa, Brazil (hinted to include all of South America), and a European coalition (named Mitteleuropa in Chapter 25, Paragraph #8). Individual nations such as Chad (the first to recognize Luna), India, and Egypt are also named.

Sources, allusions, and referencesEdit

Possible sourcesEdit

The situation depicted in the second and third part of the novel resembles the rebellion of the Lunar colony described in another science-fiction novel published in 1959, "Time Out of Joint", by Philip K. Dick. While the opposition between Earth and Moon echoes the historical conflict between the United States and the British Empire, the way the Lunar rebels force Earth to acknowledge their independence is similar to the one they adopt in Dick's novel (launching missiles, some with nuclear warheads, in an unpredictable fashion).

Allusions to other worksEdit

Professor de la Paz names Carl von Clausewitz, Niccolò Machiavelli, Oskar Morgenstern, and Che Guevara as part of a long list of authors for revolutionaries to read. He also quotes a "Chinese General" on the subject of weakening the enemy's resolve, a reference to Sun Tzu's "The Art of War".

When planning the revolution, Mike is described by Mannie as "our Scarlet Pimpernel, our John Galt, our Swamp Fox, our man of mystery", referring to the works of the Baroness Orczy and Ayn Rand as well as to the history of the American Revolution. There are intentional parallels to the American Revolution; Luna's Declaration of Independence is issued on July 4, 2076, and one event is referred to as paralleling the Boston Tea Party.

When discussing the resource loss on Luna and likelihood of ensuing food riots, Professor de la Paz suggests that Mannie read the work of Thomas Malthus.

References to other worksEdit

The setting of the novel was revisited by Heinlein in his late-period novel, "The Cat Who Walks Through Walls", as was the character Hazel Stone, who appeared as a minor character in the Lunar revolution and a central character in Heinlein's earlier book, "The Rolling Stones"/"Space Family Stone" (1952).

In "The Cat Who Walks Through Walls", the names of the signatories of the Lunar Declaration of Independence are studied; but Room L of the Raffles Hotel, wherein the revolution was plotted, is still used as an ordinary hotel room, albeit with a plaque on the wall.

References to history, geography, and scienceEdit

The lunar action takes place in Mare Crisium and the novel makes accurate references to such nearby locales as Crater Peirce. According to the narrator, most people live in one of six major underground warrens linked by tube, a system of underground trains. Luna City is the most important to the plot, and is "on the eastern edge of Mare Crisium". The Authority warren Complex Under is connected to Luna City by the Trans-Crisium tube. Johnson City is close to the complex, linked by a single tunnel. Novy Leningrad, a large warren, is linked to Luna City by tube, and a journey between the two requires the traveler to "change at Torricelli crater". Another warren is Tycho Under, whose location is clearly in the area of the crater Tycho. Hong Kong Luna is located in crater Plato. The warren known as Churchill is not described in detail, although it is linked to Hong Kong Luna via a tube across the Sinus Medii on the Lunar Prime Meridian. The secret catapult is built in the region of Mare Undarum.

Colorado Springs, Colorado is mentioned as near the military target Cheyenne Mountain which took a direct hit during the "Wet Firecracker War" but suffered little damage until hit many times by rock missiles from Luna.

The Headquarters of the Lunar Authority on Earth are in the city of Agra, near the Taj Mahal. The bombardment from Luna omits the city of Agra from its target list out of respect. Mannie, a New York Yankees fan, visits what is presumed to be Yankee Stadium, now expanded to hold at least 200,000 people; and also visits Salem, Massachusetts and Concord, Massachusetts.

Lasers are used primarily as mining and cutting tools, but are adapted as hand weapons and ground-to-orbit weapons by the Loonies.

Luna's industries use both solar power and hydrogen fusion. Heinlein correctly quotes the maximum yield of solar cells at about 1 kilowatt per square meter, but is over-optimistic with regard to fusion, describing it as taking place in small magnetic plasma pinch bottles.

Mannie refers to a comrade, Foo Moses Morris, who, following the revolution, becomes broke and starts a tailor shop in Hong Kong Luna; a reference to Robert Morris, who helped support the American revolutionary government and also suffered financial reverses.

The Brass CannonEdit

Heinlein's original title for the novel was "The Brass Cannon", replaced with the final title at the publisher's request. The original title was derived from an event in the novel.

While on Earth, Professor Bernardo de la Paz purchases a small brass cannon, originally a "signal gun" of the kind used in yacht racing. When Mannie asks him why he bought it, the Professor relates the following parable, implying that self-government is an illusion caused by failure to understand reality:

"Once there was a man who held a political make-work job like so many here...shining brass cannon around a courthouse. He did this for years...but he was not getting ahead in the world. So one day he quit his job, drew out his savings, bought a brass cannon – and went into business for himself."

Professor de la Paz asks Mannie to assure that Luna adopts a flag consisting of a brass cannon over a red bar on a black background with stars, "a symbol for all fools who are so impractical as to think they can fight City Hall". Before leaving politics, Mannie and Wyoh carry out his wish. The cannon and flag were inspired by the Battle of Gonzales (1835), an event which is seen by many as sparking the Texas Revolution.

Heinlein himself owned a small brass cannon, which he acquired prior to the 1960s. For nearly 30 years, the firing of the brass cannon, or "signal gun", was a 4th of July tradition at the Heinlein residence. It is believed that this cannon was the inspiration for Heinlein's original title for the work which eventually became "The Moon Is a Harsh Mistress". Virginia Heinlein retained the cannon after her husband's death in 1988. The cannon was eventually bequeathed to friend and science fiction writer Brad Linaweaver, after Virginia Heinlein died in 2003. Linaweaver restored the cannon to working order and subsequently posted a 2007 video of it being fired several times (with very small charges) on YouTube.