US scientists David Gross, David Politzer and Frank Wilczek have won the 2004 Nobel Prize for physics.
Atomic visualisation: Each proton or neutron is composed of three quarks
They have been honoured for their insights into the deep structure of matter - the materials that build atoms and the forces that hold them together.
The Swedish committee behind the prize said their work on quarks and the strong force brought science closer to its dream of "a theory for everything".
The physicists will each receive a medal and share of the $1.3m prize.
The honour is named after Alfred Nobel, the wealthy Swedish industrialist and inventor of dynamite.
This year's physics Nobel follows in a tradition that goes back to the very first awards in 1901, celebrating discoveries about the most fundamental constituents of the Universe.
Three decades ago, Gross, Politzer and Wilczek came up with a theory to describe the force that holds together quarks, the elementary particles with which nature constructs the neutrons and protons that make up the nuclei of atoms.
They fancifully described their force in terms of "colour", saying that quarks could be red, green or blue, rather like electrical charge can be positive or negative; and just as electrical opposites attract, so combinations of quark colour can make for stable collections of quarks.
Their theory successfully explained why quarks tended to group in threes. It also explained why, paradoxically, the "colour charge" weakens as the quarks move together and strengthens when they move apart.
It is a property that has been compared to a rubber band. The more the band is stretched, the stronger the force.
The researchers' discoveries, published in 1973, led to the theory of quantum chromodynamics, or QCD.
"This theory was an important contribution to the Standard Model, the theory that describes all physics connected with the electromagnetic force (which acts between charged particles), the weak force (which is important for the Sun's energy production) and the strong force (which acts between quarks)," the Royal Swedish Academy of Sciences said in awarding the prize.
"Thanks to their discovery, David Gross, David Politzer and Frank Wilczek have brought physics one step closer to fulfilling a grand dream, to formulate a unified theory comprising gravity as well - a theory for everything," the academy's citation added.
These ideas continue to be investigated in the world's particle accelerators.
Gross is attached to the Institute for Theoretical Physics, at the University of California-Santa Barbara; Politzer is from the California Institute of Technology; and Wilczek works at the Massachusetts Institute of Technology Center for Theoretical Physics.
On Monday, two US scientists were awarded the Nobel Prize for Medicine for uncovering the secrets of the human sense of smell.