The proceedings of DIS 2001 present the most updated status of deep inelastic scattering (DIS) physics. Topics like structure function measurements and phenomenology, QCD studies in DIS and photoproduction, spin physics and diffractive interactions are reviewed in detail, with emphasis on those studies that push the test of QCD and the Standard Model to the limits of their present range of validity, towards both the very high and the very low four-momentum transfers in the lepton-proton scattering. Moreover, this workshop coincided with the transition between the first period of experimentation at the HERA ep collider at DESY and the start of the updated HERA II operation — allowing a review of what has been learned up to now and a discussion on the main future directions of research in this field.

This workshop is the fourth of a series initiated in Durham (March 93), followed by Eilat (February 94) and Paris (April 95). The large interest and the great inflow of experimental data, coming mainly from HERA, are some of the reasons behind the decision to have this annual meeting, presently the most important one for this area of research. During the workshop, experimental results and theoretical aspects have been reported on subjects, which have been organised by working groups on: 1) hadron structure functions; 2) photoproduction and photon structure; 3) diffractive interactions; 4) hadronic final states; 5) spin effects in lepton nucleon scattering; 6) special session on theoretical advances. While the contributions to the working groups offer hot material for specialists, the reports by the conveners, as well as other contributions to the plenary sessions, offer to nonspecialists a complete overview of this research field.

The proceedings of DIS 2001 present the most updated status of deep inelastic scattering (DIS) physics. Topics like structure function measurements and phenomenology, QCD studies in DIS and photoproduction, spin physics and diffractive interactions are reviewed in detail, with emphasis on those studies that push the test of QCD and the Standard Model to the limits of their present range of validity, towards both the very high and the very low four-momentum transfers in the lepton-proton scattering. Moreover, this workshop coincided with the transition between the first period of experimentation at the HERA ep collider at DESY and the start of the updated HERA II operation -- allowing a review of what has been learned up to now and a discussion on the main future directions of research in this field.

These proceedings contain descriptions of the latest experiments and results in a variety of hot topics, such as the growth of total cross sections, the ratio of real to imaginary parts of forward scattering amplitudes, etc. Current theories of particle interaction based on QCD were presented and confronted by the latest experimental results from FNAL, CERN, HERA and elsewhere. The theoretical situation seems less clear, or at least more open to argument and criticism, leveled by the different groups responsible and present at the workshop.

This volume focusses on four main topics: structure functions, tests of quantum chromodynamics, physics at the highest Q2 and p2T, and high energy scattering and diffraction. Comprehensive review articles on hadronic and photon structure, lepton-parton and parton-parton physics as well as future experimental opportunities are presented, together with a special lecture on HERA's legacy after the first decade of operation.