The Bragg Crystal Spectrometer (BCS) is one of the instruments which makes up the scientific payload of the Yohkoh mission. The spectrometer employs four bent germanium crystals, views the whole Sun , and observes the resonance line complexes of H-like FeXXVI, CaXIX, and SXV in four narrow wavelength ranges with a resolving power (lambda/delta-lambda) of between 3000 and 6000. The spectrometer has approaching 10 times better sensitivity than that of previous instruments thus permitting a time resolution of better that 1 s to be achieved. The principal aim is the measurement of the properties of the 10 to 50 million K plasma created in solar flares with special emphasis on the heating and dynamics of the plasma during the impulsive phase.