  Starting from the Swift sample we define a complete sub-sample of 58 bright
long Gamma Ray Bursts (GRB), 55 of them (95%) with a redshift determination, in
order to characterize their properties. Our sample (BAT6) allows us to study
the properties of the long GRB population and their evolution with cosmic time.
We focus in particular on the GRB luminosity function, on the spectral-energy
correlations of their prompt emission, on the nature of dark bursts, on
possible correlations between the prompt and the X-ray afterglow properties,
and on the dust extinction.
