The postulate that consciousness causes collapse is an interpretation of quantum mechanics in which consciousness is postulated to be the main mechanism behind the process of measurement in quantum mechanics. It is a historical interpretation of quantum mechanics that is largely discarded by modern physicists. The idea is attributed to Eugene Wigner who wrote about it in the 1960s, but traces of the idea appear as early as the 1930s. Wigner later rejected this interpretation in the 1970s and 1980s.

This interpretation has been tied to the origin of pseudoscientific currents and New Age movements, specifically quantum mysticism.

According to Werner Heisenberg’s recollections in Physics and Beyond, Niels Bohr is said to have rejected the necessity of a conscious observer in quantum mechanics as early as 1927.

In his 1932 book Mathematical Foundations of Quantum Mechanics, John von Neumann argued that the mathematics of quantum mechanics allows the collapse of the wave function to be placed at any position in the causal chain from the measurement device to the "subjective perception" of the human observer. However von Neumann did not explicitly relate measurement with consciousness. In 1939, Fritz London and Edmond Bauer argued that the consciousness of the observer played an important role in measurement. However London wrote about consciousness in terms of philosophical phenomenology and not necessarily as a physical process.

The idea that "consciousness causes collapse" is attributed to Eugene Wigner who first wrote about it in his 1961 article "Remarks on the mind-body question" and developed it further during the 1960s. Wigner reformulated the Schrödinger's cat thought experiment as Wigner's friend and proposed that the consciousness of an observer is the demarcation line that precipitates collapse of the wave function, independent of any realist interpretation. The mind is postulated to be non-physical and the only true measurement apparatus.

The idea was criticized early by Abner Shimony in 1963 and by Hilary Putnam a year later.

Wigner discarded the conscious collapse interpretation in the later 1970s. In a 1982 lecture, Wigner said that his early view of quantum mechanics should be criticized as solipsism. In 1984, he wrote that he was convinced out of it by the 1970 work of H. Dieter Zeh on quantum decoherence and macroscopic quantum phenomena.

The idea of consciousness causing collapse has been promoted and developed by Henry Stapp, a member of the Fundamental Fysiks Group, since 1993.