Aerogel is synthesized using sol-gel processing followed by supercritical solvent extraction, which leaves the original gel structure virtually intact. Although aerogels have been formed from metal oxides, polymers and carbon, the most interesting composition is silica. Aerogels are meso/nanostructured, open pore materials with many unusual properties including transparency, high thermal resistance, very low refractive index and sound velocity and high surface area. One limitation, however, on current processing methods centers on the polydispersity of pore sizes in the final aerogel, thus limiting some high performance applications. Here, we see an overview of the history and uptoday usage of silica aerogels.