  This review gives an introduction to spectrometers and discusses their use
within radio astronomy. While a variety of technologies are introduced,
particular emphasis is given to digital systems. Three different types of
digital spectrometers are discussed: autocorrelation spectrometers, Fourier
transform spectrometers, and polyphase filterbank spectrometers. Given their
growing ubiquity and significant advantages, polyphase filterbanks are detailed
at length. The relative advantages and disadvantages of different spectrometer
technologies are compared and contrasted, and implementation considerations are
presented.
