Holism (from holon, a Greek word meaning entity) is the idea that the properties of a system cannot be determined or explained by the sum of its components alone. The word, along with the adjective holistic, was coined by Jan Smuts in the early 1920s. As given in the Oxford English Dictionary, Smuts defined holism as "The tendency in nature to form wholes that are greater than the sum of the parts through creative evolution."

Holism is sometimes described as the opposite to reductionism, although proponents of scientific reductionism state that it is better regarded as the opposite of greedy reductionism. It may also be contrasted with atomism. Some critics claim holism is an attempted merger of creationism (creative tendency) and evolutionism (creative evolution).

For example, in physics, certain quantum phenomena seem to arise only in systems and cannot be explained by the interaction of the system's individual parts alone. This is a suggestion -- not a fact or law. In metaphysics, phenomena such as life, mind and conscience only arise in systems. This means these things cannot be explained by the study of nerves, cells or atoms.

One theory of holism is based on the hypothesis that nature consists of a hierarchy of "wholes" (also called "holons", a term created by Arthur Koestler). These "wholes" are quarks, protons, atoms, molecules, minerals, cells, tissues, organisms, populations. Thus, a large-scale body, such as the biosphere cannot be understood by only studying the elements, but should be considered as a whole entity, studied through the different hierarchical levels, and with the different relations between the different elements.

Holism also means an object or a system can be recognised as a type, only with a few well-chosen characteristics. Hence, it is the basis of classification or typology. Soil, vegetation (land cover), biomes are commonly considered as wholes and hence can be classified using a set of diagnostic characteristics (see for example land classification).

The field of systems thinking has been developed in recent years to tackle a wide range of issues using holistic concepts.