The determination of the rate at which the Universe expands is one of 
the most crucial measurements for cosmology, since the rate at which 
it decelerates/accelerates directly depends on the energy components
which characterize the Universe (and, in particular, the "dark 
energy" in case of an accelerated expansion). To unveil the nature of 
the energy components of the Universe, it is therefore fundamental to 
constrain it very precisely. I will report a new direct determination 
of the expansion rate of the Universe H(z) up to z~1.1 with a 5-12% 
accuracy in H(z). It has been obtained from the study of the 
differential spectroscopic evolution of a large sample of early-type 
galaxies, with more than 11000 galaxies selected and extracted from 
different spectroscopic surveys to cover a wide redshift range, 
0.15<z<1.4. These measurements provide a new robust evidence of the 
accelerated expansion of the Universe, confirming a Lambda-CDM standard 
model and opening the possibility to constrain other more exotic 
cosmologies. 

I will also discuss the potentiality of the observational Hubble 
parameter H(z) in constraining cosmological parameters 
and the dark energy potential.