Recent advances in the theory of chemical and physical systems : proceedings of the 9th European Workshop on Quantum Systems in Chemistry and Physics (QSCP IX) held at Les Houches France in September 2004 Advances in the Theory of Chemical and Physical Systems is a collection of 26 selected papers from the scientific presentations made at the 9th European Workshop on Quantum Systems in Chemistry and Physics (QSCP IX) held at Les Houches France in September 2004. This volume encompasses a spectrum of developing topics in which scientists place special emphasis on theoretical methods in the study of chemical and physical properties of various systems: Quantum Chemical Methods (including CC and DFT for excited states) Relativistic and Heavy Element Systems (including radiative and nuclear effects)Complexes and Clusters (including metal complexes and clusters) Complex Systems (including quasicrystals nanotubes and proteins).