Constructivism (also known as Constructionism) is a relatively recent perspective in Epistemology that views all of our knowledge as "constructed" in that it is contingent on convention, human perception and social experience. Therefore, our knowledge does not necessarily reflect any external or "transcendent" realities.

It is considered by its proponents to be an alternative to classical Rationalism and Empiricism. The constructivist point of view is both pragmatic and relativistic in nature. It opposes Positivism and Scientism in that it maintains that scientific knowledge is constructed by scientists, and not discovered from the world through strict scientific method, and it holds that there is no single valid methodology, and that other methodologies may be more appropriate for social science.

The common thread between all forms of Constructivism is that they do not focus on an ontological reality ("reality-as-it-is-in-itself", which constructivists regard as is utterly incoherent and unverifiable), but instead on constructed reality. Thus, they reject out of hand any claims to universalism, realism or objective truth, and admit that their position is merely a view, a more or less coherent way of understanding things that has thus far worked for them as a model of the world.

Although the roots of Constructivism can be traced back to the Greek philosophers Heraclitus, Protagoras and Aristotle, it was only in 1934 that the French philosopher Gaston Bachelard (1884 - 1962) claimed that "Nothing proceeds from itself. Nothing is given. All is constructed", and only in 1967 that Jean Piaget (1896 - 1980) first used the expression "constructivist epistemology".

The doctrine is indebted to late 19th Century Darwinian theory, as it is claimed by constructivists that human understanding, as the product of Natural Selection, can be said to provide no more "true" understanding of the world as it is in itself than is absolutely necessary for human survival.

• Epistemological Constructivism is the philosophical view, as described above, that our knowledge is "constructed" in that it is contingent on convention, human perception and social experience.
• Social Constructivism (or Social Constructionism) is the theory in Sociology and Learning Theory that categories of knowledge and reality are actively created by social relationships and interactions. A social construction (or social construct) is a concept or practice which may appear to be natural and obvious to those who accept it, but in reality is an invention or artifact of a particular culture or society. Ludwig Wittgenstein's later philosophy can be seen as a foundation for Social Constructivism, with its key theoretical concepts of language games embedded in forms of life.
• Psychological Constructivism theorizes about and investigates how human beings create systems for meaningfully understanding their worlds and experiences. Personal Construct Psychology is a theory of personality developed by the American psychologist George Kelly in the 1950's that a person's unique psychological processes are channelled by the way he or she anticipates events.
• Genetic Epistemology is a type of Constructivism established by Jean Piaget (1896 - 1980) which studies of the origins (genesis) of knowledge. It purports to show that the method by which the knowledge was obtained or created affects the validity of that knowledge. For example, our direct experience of gravity makes our knowledge of it more valid than our indirect experience of black holes. If holds that change only occurs if the subject engages with experiences from outside its worldview. The theory also attempts to explain the process of how a human being develops cognitively from birth throughout his or her life, through four primary stages of development.
• Mathematical Constructivism is the view in Philosophy of Mathematics that it is necessary to find (or "construct") a mathematical object to prove that it exists. Intuitionism is a kind of Mathematical Constructivism, which maintains that the foundations of mathematics lie in the individual mathematician's intuition, thereby making mathematics into an intrinsically subjective activity.
• Constructivism is also the name of a movement in 20th Century Russian art and architecture, as well as a discipline of international relations and world affairs.