This is a compilation of manuscripts on mineral and thermal waters of different areas of the world. This special volume is devoted to the 41st Meeting of the Commission on Mineral and Thermal Waters of International Association of Hydrogeologists (IAH-CMTW) held in Cairo, Egypt, in October 2009. The presentations collected and presented in this volume show the variety of aspects of mineral and thermal waters occurrence and utilization in different countries of the world with a special focus on Egypt, Iran, Ukraine, Poland, Russia and Australia.