High-energy accelerators and colliders have been essential tools in the sea
rch for the fundamental constituents of matter and their interactions. They
have contributed greatly to the validation of the Standard Model. In the c
oming years, new data will be collected at HERA, the Tevatron and, starting
in 2005, at LHC. Considering the fruitful complementarity of hadron collid
ers and lepton colliders, it is therefore desirable to extend the centre-of
-mass energy of e(+)e(-) colliders from that presently obtained at LEP (ca,
200 GeV) into the TeV energy range, with luminosities well above 10(34) cm
(-2) s(-1). Such high energies and luminosities can only be reached using e
lectron-positron linear colliders. The physics potential of a high-energy e
(+)e(-) collider and the success of the Stanford Linear Collider have led t
o a worldwide coordinated effort to construct such a facility. Detailed des
ign work as well as the construction of large test facilities is underway a
t many major particle physics laboratories. In this review, the physics pot
ential and design of TESLA, a collider based on low-frequency superconducti
on radio frequency cavities, will be discussed.