Every cell in the human body contains the same raw genetic information, locked in our DNA.
But bone cells, nerve cells, skin cells, white blood cells, heart cells and many more each use that genetic code in different highly specialised ways.
The work by the US pair helps explain how that happens.
The medicine and physiology prize winners are selected by the Nobel Assembly of Sweden’s Karolinska Institute.
They said: “Their ground-breaking discovery revealed a completely new principle of gene regulation that turned out to be essential for multicellular organisms, including humans.
“It is now known that the human genome codes for over one thousand microRNAs.”