In particle physics, the bootstrap model, bootstrap principle or hadron boostrap is a superseded hypothesis about the composition of elementary particles interacting under the strong nuclear interaction. It uses general consistency criteria to determine the form of a quantum field theory from assumptions on the spectrum of particles. It is a form of S-matrix theory. The term is derived from bootstrapping as in 'pulling oneself up by one's bootstraps,' as particles appears from self-consistency.

It was first proposed in 1959 by Geoffrey Chew to explain particles interacting through the strong interaction. It fell out of favor in the 1970s with the rise of quantum chromodynamics, which described hadrons (mesons and baryons) in terms of elementary particles called quarks and gluons. Nevertheless, the bootstrap model was important for the development of string theory.

In 1943, Werner Heisenberg constructed a theory based on the properties of the S-matrix. While Heisenberg's program was not immediately taken seriously, during the 1950s scientists like Stanley Mandelstam, Murray Gell-Mann, Steven Frautschi and Francis E. Low used his idea to develop S-matrix theory.

In the 1960s, the ever-growing list of hadrons in the particle zoo made physicist think that the nature of the strong interaction had to be reformulated. Geoffrey Chew and Mandelstam attempted to build theory of hadrons based on S-matrix theory, rejecting standard quantum field theory. Chew used the term "bootstrap hypothesis" for the first time in 1961 considering all hadrons as manifestations of the same interaction, unaware of the work of Heisenberg. As suggested by Gell-Mann, Chew advocated for nuclear democracy, the idea that there was no hadron that was more elementary than the others. This idea was in contrast with the "aristocratic" picture of quantum electrodynamics.

In 1962, Fredrik Zachariasen and Charles Zemach used the bootstrap model to derive the properties of the rho meson, a resonance of pion scattering recently discovered in particle accelerators. They derived the mass of the rho meson to reasonable precision.

Right after, the quark model started to emerge, proposed by Gell-Mann and George Zweig in 1964, indicating that hadrons were composed of more elementary particles called quarks, but the prevailing opinion was that quarks were not physical and were just mathematical artifacts.

During the 1967 Solvay Conference, Chew and Gell-Mann presented their theories. Gell-Mann tried to connect the bootstrap model with his quark model. It was the last Solvay Conference on particle physics. Gell-Mann in general did not consider that there was a conflict between the two models.

Between 1967 and 1973, deep inelastic scattering experiments at SLAC National Accelerator Laboratory confirmed the existence of quarks and the bootstrap model was superseded by the development of quantum chromodynamics. The bootstrap theory was never refuted by experiments but it was considered unsatisfactory as it not delivered on its promises.