The concept of dignity is often used, not only by bioethicists, religious leaders, and legal theorists, but in common parlance as well. Its Latin root lies in the word dignus, which means “worthy.” Let us begin by defining this elusive term. Here are seven basic aspects of dignity, most of which are generally implicated whenever people employ the word: 
1. Individuality. Human persons are not interchangeable. Each one possesses a particular constellation of mental and physical traits, and a unique narrative history, that define that person’s distinctive personal identity.
2. Equal worth. Each human person possesses an intrinsic quality of infinite value, in equal measure with all other humans, regardless of his or her particular character, capabilities, or station in life.
3. Inalienable. This quality of value is permanent and irreversible: it cannot be degraded or removed by life events or the external actions of others. When we say, “This robs her of her dignity,” we do not really mean that the person’s dignity is being removed. What we mean is: “This action violates, constitutes an affront to, the person’s fundamental worth.”
4. Non-scalar. This quality does not come in increments or gradations: one cannot have more or less human dignity. One either is a human person, and thus possesses this quality in full, or one is not a human person, and hence does not. Even with special cases in the grey areas – e.g. comatose persons, fetuses, anencephalic persons – we are still making a judgment whether the person possesses human dignity, or none at all.
5. Ends, not means. Because they possess this quality of fundamental worth, all humans must always be treated as ends in themselves, and never as a mere means to an external end.
6. Respect. The possession of this quality commands a special measure of respect, and respectful treatment, from other people.
7. Comportment. The possession of this quality commands a special demeanor, or way of holding oneself, evincing an inner attitude of self-respect, restraint, and self-possession.
Within the legal sphere, the concept of dignity is both ubiquitous and unfailingly vague. One finds it accorded key roles in proclamations, treaties, and national constitutions, ranging from the U.N.’s Universal Declaration of Human Rights (1948) to the European Union’s Charter of Fundamental Rights (2000), from the German constitution (1949) to the Helsinki Declaration of the World Medical Association (1964). In all these cases, the concept is presented in the manner of a self-evident truth about humans: it is an axiom, a foundational element upon which other legal rights and duties can be layered.  Thus, the Universal Declaration of Human Rights, set forth by the United Nations in 1948, placed the concept at the heart of Article 1:
“All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.” 
The historian Lynn Hunt has suggested (obliquely, since she focuses on human rights rather than dignity itself) that the essential principles of the concept came to be explicitly articulated for the first time during the 18th century in Europe – though she acknowledges that some key features of it had existed among virtually all human societies long before.  She singles out the qualities of autonomy and empathy as especially important: one could not have an idea of basic rights unless humans could be seen as “separate individuals who were capable of exercising independent moral judgment,” and as kindred creatures in whom one could recognize the same types of aspirations, emotions, and experiences that one found resonating inside oneself.
Where does dignity come from? Philosophers have differed on this point.  Stoic philosophers such as Epictetus, Seneca, and Marcus Aurelius were among the first to articulate systematically the concept of equal human worth on which the broader idea of dignity rests.  Christian and Jewish thinkers have derived it from the idea that human beings are created in the image of God. Immanuel Kant believed it went hand-in-hand with our unique status as rational, moral beings, possessing free will and inhabiting a dimension of agency, duty, and responsibility. Hegel emphasized the interpersonal dimension of dignity – the fact that our human selfhood is crucially contingent on the recognition of us as conscious agents by other people around us. Many existentialists saw it as springing from our unique status as makers of meaning – creators of the framework of values we choose to affirm and live by. John Rawls implicitly places dignity at the heart of his theory of justice, since the “veil of ignorance” on which it rests is deliberately conceived as a mechanism for recognizing the fundamental equality of all citizens.
 I derive this set of qualities from discussions of dignity by the following authors: Christian Smith, What is a Person? (U. of Chicago, 2011); George Kateb, Human Dignity (Harvard, 2011); Michael Rosen, Dignity: Its History and Meaning (Harvard, 2012); Ronald Dworkin, Justice for Hedgehogs (Harvard, 2011); Michael Sandel, The Case Against Perfection: Ethics in the Age of Genetic Engineering (Harvard, 2007); Lynn Hunt, Inventing Human Rights: A History (Norton, 2007); Jürgen Habermas, The Future of Human Nature (Polity, 2003); Leon Kass, Life, Liberty and the Defense of Dignity: The Challenge for Bioethics (Encounter Books, 2002); Francis Fukuyama, Our Posthuman Future: Consequences of the Biotechnology Revolution (Farrar, Straus, 2002); Steven Pinker, The Blank Slate: The Modern Denial of Human Nature (Viking, 2002).
 See the illuminating discussion in Martha Nussbaum, Creating Capabilities: The Human Development Approach (Harvard, 2011), 129-31.