We describe the physics potential of e + e − linear colliders in this report. These machines are planned to operate in the first phase at a center-of-mass energy of 500 GeV, before being scaled up to about 1 TeV. In the second phase of the operation, a final energy of about 2 TeV is expected. The machines will allow us to perform precision tests of the heavy particles in the Standard Model, the top quark and the electroweak bosons. They are ideal facilities for exploring the properties of Higgs particles, in particular in the intermediate mass range. New vector bosons and novel matter particles in extended gauge theories can be searched for and studied thoroughly. The machines provide unique opportunities for the discovery of particles in supersymmetric extensions of the Standard Model, the spectrum of Higgs particles, the supersymmetric partners of the electroweak gauge and Higgs bosons, and of the matter particles. High precision analyses of their properties and interactions will allow for extrapolations to energy scales close to the Planck scale where gravity becomes significant. In alternative scenarios, like compositeness models, novel matter particles and interactions can be discovered and investigated in the energy range above the existing colliders up to the TeV scale. Whatever scenario is realized in Nature, the discovery potential of e + e − linear colliders and the high-precision with which the properties of particles and their interactions can be analysed, define an exciting physics programme complementary to hadron machines.

We present new sets of fragmentation functions for charged pions and kaons, both at leading and next-to-leading order. They are fitted to TPC data taken at energy √ s = 29 GeV and describe excellently a wealth of other e + e − data on charged-hadron production, ranging from √ s = 5.2 GeV way up to LEP 1 energy.They also agree with data on the production of neutral pions and kaons, if one makes the natural assumption that the respective fragmentation functions are related to the charged counterparts by SU(2) symmetry. We also list simple parameterizations of the x and Q 2 dependence of our results, which may be implemented conveniently in applications.

We present new sets of fragmentation functions for D * ± mesons, both at leading and next-to-leading order. They are determined by fitting LEP1 data on inclusive D * ± production in e + e − annihilation. In one of the sets, we take the charm-quark fragmentation function to be of the form proposed by Peterson et al. and thus obtain updated values of the c parameter and the c → D * + branching ratio. The new fragmentation functions lead to an excellent description of other e + e − data with centre-of-mass energies between 10 and 35 GeV. They also nicely agree with recent HERA data on inclusive D * ± photoproduction in ep collisions, which may be considered as a test of the universality of the fragmentation into D * ± mesons.