Silica aerogel has been widely used as a radiator for Cherenkov detectors. It is a highly porous, low-density and transparent matter with a refractive index (n) covering the range between the condensed phase (n ~ 1.3) and gases (n < 1.001). The review is devoted to the consideration of various aspects concerning aerogel: its production methods, optical and physical properties, including transparency, absorption, and scattering lengths, the number of photoelectrons and also factors affecting the accuracy of particle identification. The use of silica aerogel in various threshold Cherenkov counters including some of its prototypes and such modern and complex spectrometers as BELLE KEK, KEDR (Novosibirsk), the Alpha Magnetic Spectrometer on International Space Station (AMS) is described. Over the last years, two or more layers of monolytic and nonmonolytic aerogel blocks with different refractive indices were used in the proximity focusing RICH. The high optical quality of the up-to-date aerogel samples was favourable for using these samples in RICH (Ring Imaging CHerenkov counter) at HERMES (DESY), LHCb (CERN), AMS and some aspects of their application are described, too.

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