Post-normal science is a concept developed by Silvio Funtowicz and Jerome Ravetz, attempting to characterise a methodology of inquiry that is appropriate for cases where "facts are uncertain, values in dispute, stakes high and decisions urgent" (Funtowicz and Ravetz, 1991). It is primarily applied in the context of long-term issues where there is less available information than is desired by stakeholders.
According to a series of articles published between 1991 and 1993 post-normal science is simply an extension of situations routinely faced by experts such as surgeons or senior engineers on unusual projects, where the decisions being made are of great importance but where not all the factors are necessarily knowable. Although their work is based on science, such individuals must always cope with uncertainties, and their mistakes can be costly or lethal.
Because of this, advocates of post-normal science suggest that there must be an "extended peer community" consisting of all those affected by an issue who are prepared to enter into dialogue on it. These parties bring their "extended facts", that will include local knowledge and materials not originally intended for publication, such as leaked official information. A political case for this kind of extension of the franchise of science is made in the context of a 'democratization of expertise', but Funtowicz and Ravetz also argue that this extension is necessary for assuring the quality of the process and of the product.
In 1962, Thomas Kuhn's The Structure of Scientific Revolutions introduced the concept of normal science as part of his theory that scientific knowledge progresses through socially constructed paradigm shifts, where normal science is what most scientists do all the time and what all scientists do most of the time. The process of a paradigm shift is essentially as follows:
- from normal science (the rules are agreed upon or disagreed upon in debates that cannot be concluded; science is puzzle solving, but some contradictions in theory cannot be resolved)
- to revolutionary science (important rules are called into question; contradictions may be resolved; paradigms shift)
- to new normal science (new rules are accepted, science returns to puzzle solving under new rules).
An illustration of the theory in practice is the Copernican revolution, where Copernicus’ idea of a (sun-centered) solar system was largely ignored (not in the rules) when first introduced; then Galileo was deemed a heretic for supporting the idea (rules called into question); and finally, after a revolution in cosmology, the solar system became an obvious and foundational part of scientific knowledge (new rules).
Another example is the question of whether light is a particle or a wave. For a long time there was debate on this point. Advocates on both sides had many valid arguments based on scientific evidence but were lacking a theory that would resolve the conflict. After a revolution in thinking, it was realized that both perspectives could be true.
Physicist and policy adviser James J. Kay described post-normal science as a process that recognizes the potential for gaps in knowledge and understanding that cannot be resolved in ways other than revolutionary science. He argued that (between revolutions) one should not necessarily attempt to resolve or dismiss contradictory perspectives of the world, whether they are based on science or not, but instead incorporate multiple viewpoints into the same problem-solving process. Post-normal science is discussed by Carrozza (2015)  in relation to the concept of democratization of expertise. For this scholar two important sources in the development of Post-normal science are Jerome Ravetz's Scientific knowledge and its social problems and Silvio Funtowicz and Jerome Ravetz's Uncertainty and quality in science for policy. Additional readings of post-normal science are offered by Weingart (1997) and by Turnpenny et al, 2010.
Few mainstream scientists[who?] advocate the approaches taken by post-normal science, even among those who agree with the goals of Funtowicz and Ravetz, though the idea has gained some publicity, appearing prominently in an article published in The Guardian in March 2007. There has been recently an increased reference to post-normal science, e.g. in Nature (journal).   
- Funtowicz, S. O. and Ravetz, J. R., 1991. “A New Scientific Methodology for Global Environmental Issues”, in Costanza, R. (ed.), Ecological Economics: The Science and Management of Sustainability: 137–152. New York: Columbia University Press.
- Funtowicz, S. O. and Ravetz, J. R., 1992. “Three types of risk assessment and the emergence of postnormal science”, in Krimsky, S. and Golding, D. (eds.), Social theories of risk: 251–273. Westport, Connecticut: Greenwood.
- Funtowicz, S. and Ravetz, J., 1993. “Science for the post-normal age”, Futures, 31(7): 735-755.
- Carrozza, C. (2015). Democratizing Expertise and Environmental Governance: Different Approaches to the Politics of Science and their Relevance for Policy Analysis. Journal of Environmental Policy & Planning, 17(1), 108-126.
- Weingart, P. From “Finalization” to “Mode 2”: old wine in new bottles?. Social Science Information 36 (4), 1997. Pp. 591-613.
- Turnpenny, J., Jones, M., & Lorenzoni, I. (2010). Where now for post-normal science? A critical review of its development, definitions, and uses. Science, Technology & Human Values, 0162243910385789.
- Hulme, Mike (March 14, 2007). "The appliance of science". The Guardian.
- Gluckman P. (2014) “Policy: The art of science advice to government”. Nature, 507, 163-165.
- Grinnell, F. (2015), “Rethink our approach to assessing risk”, Nature, 522, 257.
- Nature, Editorial, (2016). “Future present”, 531, 7–8.
- Ravetz, J. R. (1986). "Usable knowledge, usable ignorance: incomplete science with policy implications." In Clark, W. C., and R. C. Munn, ed. Sustainable development of the biosphere, p. 415–432. New York: Cambridge University Press.
- Funtowicz, S.O. and J.R. Ravetz (1990). Uncertainty and quality in science for policy. Kluwer Academic Publishers, the Netherlands.