  We review and update some aspects of deuterium chemistry in the
post-recombination Universe with particular emphasis on the formation and
destruction of HD. We examine in detail the available theoretical and
experimental data for the leading reactions of deuterium chemistry and we
highlight the areas where improvements in the determination of rate
coefficients are necessary to reduce the remaining uncertainties. We discuss
the cooling properties of HD and the modifications to the standard cooling
function introduced by the presence of the cosmological radiation field.
Finally, we consider the effects of deuterium chemistry on the dynamical
collapse of primordial clouds in a simple ``top-hat'' scenario, and we
speculate on the minimum mass a cloud must have in order to be able to cool in
a Hubble time.
