The criteria for the evaluation of the REE composition of phosphorites and sedimentary rocks have been determined. These data are required to reconstruct depositional environments. Literature data on the geochemistry of some phosphorite deposits of Eurasia are considered. The REE patterns of Mesozoic phosphorites of the East European Platform are studied. On the basis of REE contents, the ratios of lanthanides and fields on the La–(Nd + Sm)–(Y + Dy), La–(Ce + Nd + Sm)–(Y + Dy), and LREE–MREE–(HREE×10) diagrams have been determined as indicators of climate and the depth and facies conditions of sedimentation.