Greatness is a concept of a state of superiority affecting a person, object, or place. Greatness can also be referred to individuals who possess a natural ability to be better than all others. The concept carries the implication that the particular person or object, when compared to others of a similar type, has clear advantage. As a descriptive term it is most often applied to a person or their work, and may be qualified or unqualified. An example of an expression of the concept in a qualified sense would be "Winston Churchill was one of the greatest wartime leaders". In the unqualified sense it might be stated "Winston Churchill achieved greatness within his own lifetime", thus implying that "greatness" is a definite and identifiable quality. Application of the terms "great" and "greatness" is dependent on the perspective and subjective judgments of those who apply them. Whereas in some cases the perceived "greatness" of a person, place or object might be agreed upon by many, this is not necessarily the case, and the perception of "greatness" may be both fiercely contested and highly individual.

Historically, in Europe, rulers were sometimes given the attribute "the Great", as in Alfred the Great and Peter the Great. The Latin equivalent "Magnus" was also used, as in Albertus Magnus and Carolus Magnus. The English language uses the Latin term magnum opus, (literally " Great work") to describe certain works of art and literature.

Since the publication of Francis Galton’s Hereditary Genius in 1869, and especially with the accelerated development of intelligence tests in the early 1900s, there has been a vast amount of social scientific research published relative to the question of ‘greatness’. Much of this research does not actually use the term ‘great’ in describing itself, preferring terms such as ‘eminence’, ‘genius’, ‘exceptional achievement’, etc. Historically the major intellectual battles over this topic have focused around the questions of ‘nature vs nurture’ or ‘person vs context’. Today the importance of both dimensions is accepted by all, but disagreements over the relative importance of each are still reflected in variations in research emphases.