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, Germany, to convene its 3^rd Sino-German conference on the theme 'Clean Energy Systems in the Subsurface: Production, Storage and Conversion'.

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:

• Integrated Energy and Environmental Utilization of Geo-reservoirs: Law, Risk Management & Monitoring
• CO₂ for Enhanced Gas and Oil Recovery, Coal Bedded Methane and Geothermal Systems
• Trapping Mechanisms and Multi-Barrier Sealing Systems for Long-Term CO₂ Storage
• Coupled THMC-Processes and Numerical Modelling
• Rock Mechanical Behaviour Considering  Cyclic Loading, Dilatancy, Damage, Self-sealing and Healing
• Underground Storage and Supply of Energy

'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.