The chemical evolution of galaxies is discussed starting with the simp
le box model. It is shown that this model with the additional assumpti
on of metal-rich outflow provides a first useful insight into the chem
ical evolution of different stellar populations. More detailed models
of galactic nucleosynthesis are then investigated which take into acco
unt galactic dynamics, non-instantaneous recycling and incomplete mixi
ng. The implications of non-instantaneous recycling on the evolution o
f the element abundances in the galactic halo are discussed and constr
aints on the evolutionary timescales of the halo are derived. Finally
a model for the formation of the galactic halo is presented which take
s into account local enrichment and incomplete mixing between differen
t gas phases.