The book presents the synthesis of silica aerogels and wide applications in industrial and other fields owing to their exceptional unique properties of silica aerogels. The silica aerogels are synthesized using different methods and the attempts have been made to reduce cost and enhance strength of silica network using various approaches. The silica aerogels are synthesized by Sol-Gel process followed by ambient pressure drying or supercritical extraction process. The experimental results on surface modification process and tuning of surface free energy of silica aerogels are demonstrated. Also the experimental details on synthesis of silica aeroges by new rapid supercritical extraction process within 3 h of total processing time, i.e. direct sol to aerogels are discussed in details.