  We show experimentally that 3-D laser cooling of lithium atoms is achieved
when the laser light is tuned exactly to resonance with the atomic transition.
For a theoretical description of this surprising phenomenon we resolve to a
full model which takes into account both the entire atomic structure and the
laser light polarization. Here we build such a model for $^7$Li atoms cooled on
the $D_{2}$-line in a $\sigma^+-\sigma^-$ laser configuration. We take all 24
Zeeman sub-levels into account and obtain good agreement with the experimental
data. Moreover, by means of Monte-Carlo simulations we show that coherent
processes play an important role in showing consistency between the theory and
the experimental results.
