“My early work is politically anarchist fiction, in that I was an anarchist for a long period of time. I'm not an anarchist any longer, because I've concluded that anarchism is an impractical ideal. Nowadays, I regard myself as a libertarian.”

The London Years (1956)

Anarchism And Other Impediments To Anarchy (1985)
Context: The history of anarchism is a history of unparalleled defeat and martyrdom, yet anarchists venerate their victimized forebears with a morbid devotion which occasions suspicion that the anarchists, like everybody else, think that the only good anarchist is a dead one. Revolution — defeated revolution — is glorious, but it belongs in books and pamphlets. In this century — Spain in 1936 and France in 1968 are especially clear cases — the revolutionary upsurge caught the official, organized anarchists flat-footed and initially non-supportive or worse. The reason is not far to seek. It's not that all these ideologues were hypocrites (some were). Rather, they had worked out a daily routine of anarchist militancy, one they unconsciously counted on to endure indefinitely since revolution isn't really imaginable in the here-and-now, and they reacted with fear and defensiveness when events outdistanced their rhetoric.
In other words, given a choice between anarchism and anarchy, most anarchists would go for the anarchism ideology and subculture rather than take a dangerous leap into the unknown, into a world of stateless liberty.

The Better Part (1901)
Context: I AM an Anarchist.
All good men are Anarchists.
All cultured, kindly men; all gentlemen; all just men are Anarchists.
Jesus was an Anarchist.
A Monarchist is one who believes a monarch should govern. A Plutocrat believes in the rule of the rich. A Democrat holds that the majority should dictate. An Aristocrat thinks only the wise should decide; while an Anarchist does not believe in government at all. Richard Croker is a Monarchist; Mark Hanna a Plutocrat; Cleveland a Democrat; Cabot Lodge an Aristocrat; William Penn, Henry D. Thoreau, Bronson Alcott and Walt Whitman were Anarchists. An Anarchist is one who minds his own business. An Anarchist does not believe in sending warships across wide oceans to kill brown men, and lay waste rice fields, and burn the homes of people who are fighting for liberty. An Anarchist does not drive women with babes at their breasts and other women with babes unborn, children and old men into the jungle to be devoured by beasts or fever or fear, or die of hunger, homeless, unhouseled and undone.
Destruction, violence, ravages, murder, are perpetrated by statute law..

Anarchism And Other Impediments To Anarchy (1985)

Anarchy (1959)

Source: Green Mars

1975 Statement to Judith Merrill, who had called herself a democrat and a libertarian, stating that such terms described him as well, as quoted in Robert A. Heinlein : In Dialogue with His Century, Volume 2: The Man Who Learned Better | 1948-1988 (2014), p. 389
Context: I think that describes me, too — still a democrat not because I love the Common Peepul and not because I think democracy is so successful (look around you) but, because in a lifetime of thinking about it and learning all that I could, I haven't found any other political organization that worked as well.
As for libertarian, I've been one all my life, a radical one. You might use the term "philosophical anarchist" or "autarchist" about me, but "libertarian" is easier to define and fits well enough.

Note to the article 'Individualism and Anarchism' by Adams (1924)
Context: I claimed that "individualist anarchism and communist anarchism are the same, or nearly so, in terms of moral motivations and ultimate goals".
I know that one could counter my claim with hundreds of texts and plenty of deeds of self-proclaimed individualist anarchists, which would demonstrate that individualist anarchist and communist anarchist are separated by something of a moral abyss.
However, I deny that that kind of individualists can be included among anarchists, despite their liking for calling themselves so.
If anarchy means non-government, non-domination, non-oppression by man over man, how can one call himself anarchist without lying to himself and the others, when he frankly claims that he would oppress the others for the satisfaction of his Ego, without any scruple or limit, other than that drawn by his own strength? He can be a rebel, because he is being oppressed and he fights to become an oppressor, as other nobler rebels fight to destroy any kind of oppression; but he sure cannot be anarchist. He is a would-be bourgeois, a would-be tyrant, who is unable to accomplish his dreams of dominion and wealth by his own strength and by legal means, and therefore he approaches anarchists to exploit their moral and material solidarity.
Therefore, I think the question is not about "communists" and "individualists", but rather about anarchists and non-anarchists. And we, or at least many of us, were quite wrong in discussing a certain kind of alleged "anarchist individualism" as if it really was one of the various tendencies of anarchism, instead of fighting it as one of the many disguises of authoritarianism.

Source: Violence and the Labor Movement (1914), p. 95-96
Context: We seek to terrorize them, as they seek to terrorize us. As the anarchist believes that oppression may be ended by the murder of the oppressor, so society cherishes the thought that anarchism may be ended by the murder of the anarchist. Are not our methods in truth the same, and can any man doubt that both are equally futile and senseless? Both the anarchy of the powerful and the anarchy of the weak are stupid and abortive, in that they lead to results diametrically opposed to the ends sought.