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The Fields Medal is a prize awarded to up to four mathematicians (not over forty years of age) at each International Congress of International Mathematical Union, since 1936 and regularly since 1948 at the initiative of the Canadian mathematican John Charles Fields. The purpose is to give recognition and support to young mathematical researchers having already made important contributions.
The Fields Medal is often described as the "Nobel Prize of mathematics". The comparison is not very accurate, in particular because the age limit is applied strictly. Fields Medals are awarded for a body of work, rather than for a particular result, though there is clearly consensus that some individual theorems can and should be recognised in this way. (That is not to say that some awards from the past have not been in some ways contentious or controversial—they have.) Since the institution of the Wolf Prizes, there has been a high-profile "lifetime achievement" award in mathematics; this has to some extent redressed perceived imbalances in the weight given to different kinds of merit and the movements of intellectual fashion across mathematics as a whole.