Macrocosm and microcosm refers to a vision of cosmos where the part (microcosm) reflects the whole (macrocosm) and vice versa. It is a feature present in many esoteric models of philosophy, both ancient and modern.^[2] It is closely associated with Hermeticism and underlies practices such as astrology, alchemy and sacred geometry with its premise of "As Above, So Below".^[3]

The philosophy was conceptualized by Pythagoras, who saw the cosmos and the body as a harmonious unity.^[4] The idea was re-articulated about a century later by Plato,^[5] and again during the Renaissance, by Leonardo da Vinci, who noted common features between the natural world and the human body such as the circulation of liquids and basic branching mechanisms.^[6]

In modern sociology, the concept of microcosm has been predominantly used to describe a small group of individuals whose behavior is typical of a larger social body encompassing it. A microcosm can be seen as a special kind of epitome. Conversely, a macrocosm is a social body made of smaller compounds. In physics, scale invariance describes the same phenomenon.