The high-frequency peaked BL Lac PKS 2155-304, the lighthouse of the Southern hemisphere sky at VHE gamma-ray energies, has been followed by the H.E.S.S. array of atmospheric Cherenkov telescopes since the first light of the project, first with a single telescope in 2002, then with two & three telescopes in 2003, and since 2004 with the full-sensitivity four-telescope array. In this mode, a number of multi-wavelength campaigns have been performed with observations from the Rossi X-ray Timing Explorer (RXTE), Rotse (Optical), Spitzer (IR), James Clark Maxwell Telescope (JCMT, sub-mm) and others in both quiescent and active states, based on both fixed campaigns and triggers from H.E.S.S. Here we present the results of this series of observations up to 2005 inclusive, together with the implications for source models of the spectral measurements and search for correlated variability with X-rays, Optical, and IR measurements. The exceptional flare activity of 2006 will be covered in a separate paper.

for the H.E.S.S. collaboration

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 3 (OG part 2), pages 985-988