Beauty is commonly described as a feature of objects that makes them pleasurable to perceive. Such objects include landscapes, sunsets, humans and works of art. Beauty, art and taste are the main subjects of aesthetics, one of the fields of study within philosophy. As a positive aesthetic value, it is contrasted with ugliness as its negative counterpart.

One difficulty in understanding beauty is that it has both objective and subjective aspects: it is seen as a property of things but also as depending on the emotional response of observers. Because of its subjective side, beauty is said to be "in the eye of the beholder". It has been argued that the ability on the side of the subject needed to perceive and judge beauty, sometimes referred to as the "sense of taste", can be trained and that the verdicts of experts coincide in the long run. This suggests the standards of validity of judgments of beauty are intersubjective, i.e. dependent on a group of judges, rather than fully subjective or objective.

Conceptions of beauty aim to capture what is essential to all beautiful things. Classical conceptions define beauty in terms of the relation between the beautiful object as a whole and its parts: the parts should stand in the right proportion to each other and thus compose an integrated harmonious whole. Hedonist conceptions see a necessary connection between pleasure and beauty, e.g. that for an object to be beautiful is for it to cause disinterested pleasure. Other conceptions include defining beautiful objects in terms of their value, of a loving attitude toward them or of their function.

Beauty, together with art and taste, is the main subject of aesthetics, one of the major branches of philosophy. Beauty is usually categorized as an aesthetic property besides other properties, like grace, elegance or the sublime. As a positive aesthetic value, beauty is contrasted with ugliness as its negative counterpart. Beauty is often listed as one of the three fundamental concepts of human understanding besides truth and goodness.

Objectivists or realists see beauty as an objective or mind-independent feature of beautiful things, which is denied by subjectivists. The source of this debate is that judgments of beauty seem to be based on subjective grounds, namely our feelings, while claiming universal correctness at the same time. This tension is sometimes referred to as the "antinomy of taste". Adherents of both sides have suggested that a certain faculty, commonly called a sense of taste, is necessary for making reliable judgments about beauty. David Hume, for example, suggests that this faculty can be trained and that the verdicts of experts coincide in the long run.

Beauty is mainly discussed in relation to concrete objects accessible to sensory perception. It has been suggested that the beauty of a thing supervenes on the sensory features of this thing. It has also been proposed that abstract objects like stories or mathematical proofs can be beautiful. Beauty plays a central role in works of art and nature.

An influential distinction among beautiful things, according to Immanuel Kant, is that between adherent beauty (pulchritudo adhaerens) and free beauty (pulchritudo vaga). A thing has adherent beauty if its beauty depends on the conception or function of this thing, unlike free or absolute beauty. Examples of adherent beauty include an ox which is beautiful as an ox but not beautiful as a horse or a photograph which is beautiful, because it depicts a beautiful building but that lacks beauty generally speaking because of its low quality.

Judgments of beauty seem to occupy an intermediary position between objective judgments, e.g. concerning the mass and shape of a grapefruit, and subjective likes, e.g. concerning whether the grapefruit tastes good. Judgments of beauty differ from the former because they are based on subjective feelings rather than objective perception. But they also differ from the latter because they lay claim on universal correctness. This tension is also reflected in common language. On the one hand, we talk about beauty as an objective feature of the world that is ascribed, for example, to landscapes, paintings or humans. The subjective side, on the other hand, is expressed in sayings like "beauty is in the eye of the beholder".