The determinations of the Boltzmann constant

The international community started recently to look for a new way to define the Kelvin. Different experiments around the world have begun. This presentation will describe very briefly the four different techniques currently used for the redetermination of k, namely the measurement of the speed of sound in pure helium-4, the determination deduce of the Doppler profile of the linear absorption line, the measurement of the noise power in an electrical resistance and finally the change of refractive index in function of the density of pure helium-4.