Abstract A review is given of certain aspects of the single-impurity Kondo problem and of the conduction-electron induced (“RKKY”) interaction between two magnetic impurities in a metallic host. The latter can be shown to exhibit a Kondo-like crossover at low temperature. The relevant temperature scale is described. A description of the scaling regimes and the crossovers in this problem is given; they depend on the sign and magnitude of the RKKY coupling. A comparison with numerical calculations is made and the connection of temperature scales and coherence in the two-impurity problem to phenomena in dense Kondo system is made.