The magnetic properties of individual atoms adsorbed on metal and insulating substrates can differ dramatically. While an atom on an insulating substrate can maintain some basic properties such as a free spin, such a free spin is strongly screened by a metal's conduction electrons when the atom is placed directly on the metal. This screening gives rise to the Kondo effect. Scanning Tunneling Microscopy was used to probe the magnetic properties of atoms adsorbed on metals and thin insulating substrates. We find spin-flip spectroscopy for Mn adsorbed on thin aluminum oxide with no sign of Kondo effect. On the other hand Co atoms on Cu substrates show a clear Kondo resonance around the Fermi energy with no sign of spin-flip spectroscopy. Mn atoms very close to the edge of an aluminum oxide patch can recover the Kondo effect albeit with very small Kondo temperatures because of their relative proximity to the conduction electrons of the underlying metal. [DOI: 10.1380/ejssnt.2006.384]