We present examples where the seismic noise records are used to image the Earth at various scales. Furthermore, these records can be used to monitor changes of elastic properties of the crust. We discuss why and how it is possible to perform high precision monitoring, even without a precise description of the noise. We analyze the effect of an anisotropic intensity of incident noise with temporal variations of azimuthal distribution. Our results indicate that high precision monitoring (fractional seismic wave variation of the order of $10^-4$) can be achieved from noise analysis in presence of a fluctuating noise. We show that the elastic properties at depth change in response to external forcing such as precipitation, temperature variations, tides, and hydraulic load. We present an application in the context of geothermal stimulation of noise based monitoring associated with a massive deep water injection in an urban area. We also use the massive data set produced by the Japanese network to show the evolution in space and time of the seismic velocity in the crust associated with the M9 Tohoku earthquake over a large part of Japan.