Stuart Hameroff (born July 16, 1947) is an American anesthesiologist and professor at the University of Arizona known for his studies of consciousness and his controversial contention that consciousness originates from quantum states in neural microtubules. He is the lead organizer of the Science of Consciousness conference.

Hameroff received his BS degree from the University of Pittsburgh and his MD degree from Hahnemann University Hospital, where he studied before it became part of the Drexel University College of Medicine. He took an internship at the Tucson Medical Center in 1973. From 1975 onwards, he has spent the whole of his career at the University of Arizona, becoming professor in the Department of Anesthesiology and Psychology and director for the Center for Consciousness Studies, both in 1999, and finally Emeritus professor for Anesthesiology and Psychology in 2003.

At the very beginning of Hameroff's career, while he was at Hahnemann, cancer-related research work piqued his interest in the part played by microtubules in cell division, and led him to speculate that they were controlled by some form of computing. It also suggested to him that part of the solution of the problem of consciousness might lie in understanding the operations of microtubules in brain cells, operations at the molecular and supramolecular level.

Hameroff's first book Ultimate Computing (1987) argues that microtubes allow for computation sufficient to explain consciousness. The main substance of this book dealt with the scope for information processing in biological tissue and especially in microtubules and other parts of the cytoskeleton. Hameroff argued that these subneuronal cytoskeleton components could be the basic units of processing rather than the neurons themselves. The book was primarily concerned with information processing, with consciousness a secondary consideration.

Separately from Hameroff, the English mathematical physicist Roger Penrose had published his first book on consciousness, The Emperor's New Mind, in 1989. On the basis of Gödel's incompleteness theorems, he argued that the brain could perform functions that no computer or system of algorithms could. From this it could follow that consciousness itself might be fundamentally non-algorithmic and therefore impossible to model as a classical Turing machine type of computer. This conflicts with the idea that consciousness is explainable mechanistically, the prevailing view among neuroscientists and those artificial intelligence researchers who support the "Strong AI" hypothesis as in the Chinese room thought experiment.^{[citation needed]}

Penrose saw the principles of quantum theory as providing an alternative process through which consciousness could arise. He further argued that this non-algorithmic process required a new form of the quantum wave reduction, later given the name objective reduction (OR), which could link the brain to the fundamental spacetime geometry.

Hameroff was inspired by Penrose's book to contact Penrose regarding his own theories about the mechanism of anesthesia, and how it specifically targets consciousness via action on neural microtubules. The two met in 1992, and Hameroff suggested that the microtubules were a good candidate site for a quantum mechanism in the brain. Penrose was interested in the mathematical features of the microtubule lattice, and over the next two years the two collaborated in formulating the orchestrated objective reduction (Orch-OR) model of consciousness. Following this collaboration, Penrose published his second consciousness book, Shadows of the Mind (1994).

Over the years since 1994, Hameroff has been active in promoting the Orch-OR model of consciousness through his web site and lectures.