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The non-perturbative parton distributions in hadrons are derived from simple physical arguments resulting in an analytical expression for the valence parton distributions. The sea partons arise mainly from pions in hadronic fluctuations. The model gives new insights and a good description of structure function data. Hard processes involving hadrons are calculated by folding perturbative QCD matrix elements with parton distributions describing the probability of finding a quark or a gluon in the hadron. Perturbative QCD evolution describes the dependence of the parton distributions on the hard scale Q of the interaction. However, their dependence on the momentum fraction x at the lower limit for applying perturbative QCD, Q 0 ≈ 0.5−2 GeV, are fitted to data using parameterisations, e.g. of the form [ 1, 2, 3] f i (x, Q 0) = N i x ai (1 − x) bi (1 + c i √ x + d i x) (1) The parameters in these functions have no direct physical meaning, making it difficult to interpret the results. To gain understanding of non-perturbative QCD we have developed a physical model [ 4] for the parton distributions at Q 0. This is here briefly described together with our latest developments. The basic physical picture is that a probe with large resolution, compared to the hadron size, will see free quarks and gluons in quantum fluctuations of the hadron. The measuring time is short compared to the lifetime of the fluctuation since the latter is determined by the confinement of quarks and gluons inside the hadron, as illustrated in Fig. 1. This makes it possible to describe the formation of the fluctuations independently of the measuring process. Hadron lifetime t=d/c Remnant Probe Parton Figure 1. Fluctuation of a hadron into a parton and a remnant. k q p r j probe Figure 2. Kinematics for scattering on a parton in a hadron. Our approach only intends to provide the four-momentum k of a single probed parton. All other information in the hadron wave function is neglected , treating the other partons collectively as a remnant with four-momentum r, see Fig. 2. It is convenient to describe the process in the hadron rest frame where there is no preferred direction and hence spherical symmetry. The probability distribution for finding one parton is taken