Evolutionism refers to theories of evolution, specifically to a widely held 19th century belief that organisms are intrinsically bound to improve themselves, and that changes are progressive and arise through inheritance of acquired characters, as in Lamarckism. The belief was extended to include cultural evolution and social evolution.The term is sometimes also used to refer to acceptance of the modern evolutionary synthesis, a scientific theory that describes how biological evolution happened. In addition, the term is used in a broader sense as a world-view covering a wide variety of topics, including chemical evolution as an alternative term for abiogenesis or for nucleosynthesis of chemical elements, galaxy formation and evolution, stellar evolution, spiritual evolution, technological evolution and universal evolution, which seeks to explain every aspect of the world in which we live.

In the modern scientific community the term is an anachronism and is considered redundant as the overwhelming majority of scientists accept evolution, and so it is not used. To say someone is a scientist implies evolutionary views. In the creation-evolution controversy, creationists often call those who accept the validity of the modern evolutionary synthesis "evolutionists" and the theory itself as "evolutionism." Some creationists and creationist organizations, such as the Institute of Creation Research, use these terms in an effort to make it appear that evolutionary biology is a form of secular religion