  The high-frequency peaked BL Lac PKS 2155-304 at redshift z=0.117 has been
detected with high significance (~45 sigma) at energies greater than 160 GeV,
using the H.E.S.S. stereoscopic array of imaging air-Cherenkov telescopes in
Namibia. A strong signal is found in each of the data sets corresponding to the
dark periods of July and October, 2002, and June-September, 2003. The observed
flux of VHE gamma rays shows variability on time scales of months, days, and
hours. The monthly-averaged integral flux above 300 GeV varies between 10% and
60% of the flux observed from the Crab Nebula. Energy spectra are measured for
these individual periods of data taking and are characterized by a steep power
law with a time-averaged photon index of 3.32 +/- 0.06. An improved chi-square
per degree of freedom is found when either a power law with an exponential
cutoff energy or a broken power law are fit to the time-averaged energy
spectrum. However, the significance of the improvement is marginal (~2 sigma).
The suggested presence of features in the energy spectrum may be intrinsic to
the emission from the blazar, or an indication of absorption of TeV gamma rays
by the extragalactic infrared background light.
