An outstanding international scientific event in the field of metathesis chemistry, the NATO ASI "Green Metathesis Chemistry: Great Challenges in Synthesis, Catalysis and Nanotechnology" has been recently organized in Bucharest, Romania (July 21- August 2, 2008). Numerous renowned scientists, young researchers and students, convened for two weeks to present and debate on the newest trends in alkene metathesis and identify future perspectives in this fascinating area of organic, organometallic, catalysis and polymer chemistry with foreseen important applications in materials science and technology. Following the fruitful practice of NATO Advanced Study Institutes, selected contributions covering plenary lectures, short communications and posters have been compiled in this special volume dedicated to this successful convention on green metathesis chemistry. General interest was primarily focused on relevant "green chemistry" features related to all types of metathesis reactions (RCM, CM, enyne metathesis, ADMET and ROMP). Diverse opportunities for green and sustainable technologies and industrial procedures based on metahesis have been identified. Largely exemplified was the utility of this broadly applicable strategy in organic synthesis, for accessing natural products and pharmaceuticals, and also its ability to fit in the manufacture of smart and nanostructured materials, self-assemblies with nanoscale morphologies, macromolecular engineering.