In this chapter we present the analysis of the large scale matter distribution within linear perturbation theory in a fully relativistic way. We take into account that only directions and redshifts are observable while lengths scales are always inferred from a cosmological model. We first introduce the traditional density and redshift space distortion contribution to the observed uctuations and then proceed to discuss the smaller lensing and large scale relativistic terms. We express the clustering properties of matter in terms of directly observable quantities and study their scale and redshift dependence. We also discuss ‘intensity mapping’ a new observational technique which will hopefully bear fruit in the near future. Also this chapter has been newly added in the second edition.