Authenticity is a concept of personality in the fields of psychology, existential psychotherapy, existentialist philosophy, and aesthetics. In existentialism, authenticity is the degree to which a person takes ownership of their choices and identity, acting in recognition of their freedom and responsibility, rather than deferring that responsibility to social roles, norms, or external authorities. The conscious self comes to terms with the condition of Geworfenheit, of having been thrown into an absurd world (without values and meaning) not of their own making, thereby encountering external forces and influences different from and other than the Self. Authenticity has emerged as a central concept in contemporary models of well-being and the good life, serving as a foundational principle in many leading psychological frameworks. A person’s lack of authenticity is considered bad faith in dealing with other people and with one's self; thus, authenticity is in the instruction of the Oracle of Delphi: “Know thyself.” Concerning authenticity in art, the philosophers Jean Paul Sartre and Theodor Adorno held opposing views and opinions about jazz, a genre of American music; Sartre said that jazz is authentic and Adorno said that jazz is inauthentic. Many musical subcultures require artistic authenticity, lest the community consider an artist to be a poseur for lacking authenticity (creative, musical, or personal); artistic authenticity is integral to many genres of music, including but not limited to genres of rock (such as punk rock and heavy metal), club music (such as house and techno), and hip-hop.

In the late 18th and early 19th centuries, Romantic thinkers emphasized intuition, emotion, and a return to nature as responses to Enlightenment rationalism, anticipating later philosophical concerns with authenticity and individual self-expression. In the 20th century, Anglo–American preoccupations with authenticity centered on the writings of existentialist philosophers whose native tongue is not English; therefore, the faithful, true, and accurate translation of the term existentialism was much debated, to which end the philosopher Walter Kaufmann assembled a canon of existentialist philosophers. Kaufmann's canon includes the Dane Søren Kierkegaard (1813–1855), the German Martin Heidegger (1889–1976), and the Frenchman Jean-Paul Sartre (1905–1980). For these existentialists, the conscious Self comes to terms with existence (being and living) in an absurd, materialist world featuring external forces, e.g. Geworfenheit (Thrown-ness), and intellectual influences different from and other than the Self.

Personal authenticity is exhibited in how a person acts and changes in response to the external world's influences upon the Self. Among artists, authenticity in art describes a work of art faithful to the artist's values. In the field of psychology, authenticity identifies a person living life in accordance with their true Self and personal values rather than according to the external demands of society, such as social conventions, kinship, and duty.

To identify, describe, and define authenticity, existential philosophers like Kierkegaard, Nietzsche, and Martin Heidegger investigated the existential and ontological significance of the social constructs that compose the norms of society. For a journalist, not blindly accepting social norms contributes to producing intellectually authentic reportage, achieved by the reporter choosing to be true to their professional ethics and personal values. Yet, in the praxis of journalism, the reporter’s authenticity (professional and personal) is continually contradicted by the business requirements of corporate publishing.

According to Søren Kierkegaard, personal authenticity depends upon inwardness and the individual’s subjective relationship to truth, particularly in matters of faith. Kierkegaard criticizes the conformity of “the crowd” and the levelling effects of modern society, arguing that individuals often lose themselves in public opinion rather than taking responsibility for their own existence. In Practice in Christianity (1850), he emphasizes that authentic faith requires the individual to stand alone before God, accepting the risks and responsibilities of personal commitment rather than relying on social convention or institutional religion. He writes:

Therefore, it is a risk to preach, for as I go up into that holy place — whether the church is packed or as good as empty, whether I, myself, am aware of it or not, I have one listener more than can be seen, an invisible listener, God in heaven, whom I certainly cannot see, but who truly can see me.... Truly, it is a risk to preach! Most people, no doubt, have the idea that stepping out on the stage as an actor to venture into the danger of having all eyes focused on one requires courage. Yet, in one sense, this danger, like everything on the stage, is an illusion because the actor, of course, is personally outside it all; his task is precisely to deceive, to dissemble, to represent someone else, and to reproduce, accurately, someone else’s words. On the other hand, the proclaimer of Christian truth steps forward into a place where, even if the eyes of all are not focused on him, the eye of an omniscient one is. His task is: to be himself, and in a setting, God’s house, which, all eyes and ears, requires only one thing of him — that he should be himself, be true. That he should be accurate, that is, that he, himself, should be what he proclaims [to be], or at least strive to be that, or at least be honest enough to confess, about himself, that he is not that.... How risky it is to be the I who preaches, the one speaking, an I who, by preaching and as he preaches, commits himself unconditionally, displays his life so that, if possible, one could look directly into his soul — to be this I, that is risky!

— Søren Kierkegaard, Practice in Christianity (1850) pp. 234–235

Personal authenticity can be achieved—without religion, which requires accepting pre-determined virtues (eternal valuations) as unquestionably true. In living authentically, a person elevates himself/herself above the mass culture to transcend the limits of conventional morality, thereby personally determining what is and what is not good and bad, without the pre-determined virtues of conformity “on account of which we hold our grandfathers in esteem”. An authentic life is achieved by avoiding the “herding animal morality”. To “stand alone [is to be] strong and original enough to initiate opposite estimates of value, to transvaluate and invert ‘eternal valuations’”. Common to the existential perspectives of Kierkegaard and Nietzsche are “the responsibilities they place on the individual to take an active part in the shaping of one’s beliefs, and then to be willing to act on that belief”.