The Nobel Prize for Chemistry has been awarded to US scientists Eric Betzig and William E Moerner, and German chemist Stefan W Hell, for developing the optical microscope into a nanoscope.
Their work has enabled modern chemists to study molecules and other substances at the nano-scale.
For some time, optical microscopes were held back because of a presumed limitation that they could never obtain a better resolution than half the wavelength of light.
However, using fluorescent molecules, the three winners of this year's prize found a way to get around that limitation.
In 2000, Professor Hell discovered that two laser beams could be used to stimulate fluorescent molecules to glow, and then cancel out all fluorescence except for that in a nanometre-sized volume.
Six years later, Professor Betzig and Professor Moerner devised a second method, which turns the fluorescence of individual molecules on and off.
As a result, the Nobel Foundation said, scientists can now visualise the pathways of individual molecules inside living cells.
Researchers can now, for example, see how molecules create junctions between nerve cells in the brain; track proteins involved in Parkinson's, Alzheimer's and Huntington's diseases; and can follow individual proteins in fertilised eggs as they divide into embryos.
Professor Betzig is Group Leader at Janelia Farm Research Campus, Howard Hughes Medical Institute, in Virginia.
Professor Moerner is based at Stanford University.
Professor Hell is Director at the Max Planck Institute for Biophysical Chemistry in Göttingen and Division head at the German Cancer Research Center, Heidelberg.
Speaking by phone to the press conference at which the announcement was made, Professor Hell said he was totally surprised to win the prize.
He said their work had proven very important for understanding physiology and disease at the cellular level.
Beautiful drawing of the #nobelprize2014 Laureates in Chemistry. pic.twitter.com/48ExczgJIm
— The Nobel Prize (@NobelPrize) October 8, 2014#nobelprize2014 #Chemstry The principle of single-molecule microscopy: pic.twitter.com/hbDhsKOTaK
— The Nobel Prize (@NobelPrize) October 8, 2014