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Rice husk is an important byproduct from the milling process of paddy rice, with a huge amount being produced worldwide each year. Silica exits abundantly in rice husk in an amorphous form. Hence, rice husk is a natural and renewable biomass source for extraction of silica and subsequently for manufacturing value-added, silicon-based materials. Currently, most rice husk is combusted directly to produce power or electricity resulting in the production of a large quantity of rice husk ash. Only a small amount of rice husk is used for extraction of silica in an industrial scale. This chapter presents a general review on the physicochemical properties of rice husk and rice husk ash, and their application as adsorbents in vegetable oil refining and removal of heavy metals. Different processing methods for production of silica and silica aerogel from rice husk ash, and the factors that influenced the physical and chemical properties of these products, are also addressed.