Current observational data point towards a "concordance" model of cosmology which, at present, has significant contributions to the total energy density from both dark matter and dark energy. Early epochs in the evolution of the Universe harbor valuable clues to the nature of the dark matter/energy, but they are shrouded by the huge optical depth of the pre-recombination plasma and can only be explored indirectly through the comparisons between observations and the predictions of primordial nucleosynthesis (BBN) and of the temperature fluctuations in the spectrum of the cosmic microwave background radiation (CMB). I will describe how BBN and the CMB together have the potential to distinguish among, or at least constrain, competing models for the dark energy, some of which leave the strength of gravity invariant while adding to the relativistic energy density, while others may modify both.