Coherent backscattering (CBS) of light waves by a random medium is a signature of
interference effects in multiple scattering. This effect has been studied in many systems
ranging from white paint to biological tissues. Recently, we have observed CBS from a
sample of laser-cooled atoms, a scattering medium with interesting new properties. In this
paper we discuss various effects which have to be taken into account for a quantitative study
of coherent backscattering of light by cold atoms.