The¿4thCologne-Bonn-ZermattSymposium: TheDenseInterstellarMedium in Galaxies¿ took place in Zermatt, Switzerland, from September 22nd to 26th, 2003. This symposium continued the series of conferences on the dense interstellar medium which has been organized every 5 years since 1988 by the I. Physikalisches Institut der Unversit¿ at ¿ zuKoln. ¿ Re?ecting the by now well established and fruitful collaboration between the MPI ffur ¿ ¿ Radioastronomie, the Radioastronomisches Institut der Universit¿ at ¿ Bonn and the I. Physikal- ches Institut der Universit¿ at ¿ zu Koln ¿ in the context of the Sonderforschun- bereich 494 ¿The Evolution of Interstellar Matter: THz- Spectroscopy in the Laboratory and in Space¿, the