  Studies of elemental abundances in stars belonging to the thin and the thick
disk of our Galaxy are reviewed. Edvardsson et al. (1993) found strong evidence
of [alpha/Fe] variations among F and G main sequence stars with the same [Fe/H]
and interpreted these differences as due to radial gradients in the star
formation rate in the Galactic disk. Several recent studies suggest, however,
that the differences are mainly due to a separation in [alpha/Fe] between thin
and thick disk stars, indicating that these populations are discrete Galactic
components, as also found from several kinematical studies. Further evidence of
a chemical separation between the thick and the thin disk is obtained from
studies of [Mn/Fe] and the ratio between r- and s-process elements. The
interpretation of these new data in terms of formation scenarios and time
scales for the disk and halo components of our Galaxy is discussed.
