  Chemical models have been developed over the years by astrophysicists to
study the pro- cesses at play in the various environments of the interstellar
medium (ISM) that define the chemical composition of the gas and the dust.
These qualitative aspects of the model predictions have been improved from a
chemical point of view thanks to many recent developments of the experimental
technics and theoretical methods that aim at studying the individual reactions
in conditions as close to the ISM conditions as possible and characterize the
rate constants of their efficiency. These models have also been more and more
associated with dynamical evolution of the ISM physical conditions (for star
forming regions for instance) since the chemical composition is far from
steady-state in such regions. In this paper, we try to assess the state of the
art concerning the chemical modeling of dark clouds, the initial step for the
formation of stars and disks.
