  A huge amount of good quality astrophysical data converges towards the
picture of a spatially flat universe undergoing the today observed phase of
accelerated expansion. This new observational trend is commonly addressed as
Precision Cosmology. Despite of the quality of astrophysical surveys, the
nature of dark energy dominating the matter-energy content of the universe is
still unknown and a lot of different scenarios are viable candidates to explain
cosmic acceleration. Methods to test these cosmological models are based on
distance measurements and lookback time toward astronomical objects used as
standard candles. I discuss the characterizing parameters and constraints of
three different classes of dark energy models pointing out the related
degeneracy problem which is the signal that more data at low (z= 0- 1), medium
(1<z<10) and high (10 <z< 1000) redshift are needed to definitively select
realistic models.
