  We have determined the luminosity function of 250um-selected galaxies
detected in the ~14 sq.deg science demonstration region of the Herschel-ATLAS
project out to a redshift of z=0.5. Our findings very clearly show that the
luminosity function evolves steadily out to this redshift. By selecting a
sub-group of sources within a fixed luminosity interval where incompleteness
effects are minimal, we have measured a smooth increase in the comoving 250um
luminosity density out to z=0.2 where it is 3.6+1.4-0.9 times higher than the
local value.
