<p>Anthropogenic greenhouse gas emissions, energy security and sustainability are three of the greatest contemporary global challenges today. This year the Sino-German Cooperation Group "Underground Storage of CO₂ and Energy", is meeting on the 21-23 May 2013 for the second time in Goslar, German<b>y</b>, to convene its 3^rd Sino-German conference on the theme "Clean Energy Systems in the Subsurface: Production, Storage and Conversion".</p><p> </p><p>This volume is a collection of diverse quality scientific works from different perspectives elucidating on the current developments in CO₂ geologic sequestration research to reduce greenhouse emissions including measures to monitor surface leakage, groundwater quality and the integrity of caprock, while ensuring a sufficient supply of clean energy. The contributions herein have been structured into 6 major thematic research themes: </p><ul><li>Integrated Energy and Environmental Utilization of Geo-reservoirs: Law, Risk Management ' Monitoring</li><li>CO₂ for Enhanced Gas and Oil Recovery, Coal Bedded Methane and Geothermal Systems</li><li>Trapping Mechanisms and Multi-Barrier Sealing Systems for Long-Term CO₂ Storage</li><li>Coupled THMC-Processes and Numerical Modelling</li><li>Rock Mechanical Behaviour Considering Cyclic Loading, Dilatancy, Damage, Self-sealing and Healing</li><li>Underground Storage and Supply of Energy</li></ul><p>"Clean energy systems in the subsurface" will be invaluable to researchers, scientists and experts in both academia and industry trying to find a long lasting solution to the problems of global climate change, energy security and sustainability.</p><p> </p><p> </p>