An acid that is stronger than the acid strength of 100% sulphuric acid is known as a superacid. Environmental concerns about the use of toxic liquid superacids and liquid inorganic acids in the transformation of hydrocarbons provide an impetus for a search of stable and more environmentally friendly solid acid catalysts. This book examines an important opportunity related to green chemistry where solid superacids lead to new gas- and liquid-solid phase reactions, which are environmentally benign processes in the chemical industry.