  The Arecibo Legacy Fast ALFA (ALFALFA) survey is an on-going second
generation blind extragalactic HI survey exploiting Arecibo's superior
sensitivity, angular resolution and digital technology to conduct a census of
the local HI universe over a cosmologically significant volume. As of mid-2007,
~4500 good quality extragalactic HI line sources have been extracted in ~15% of
the final survey area. ALFALFA is detecting HI masses as low as 10**6 Msun and
as high as 10**10.8 Msun with positional accuracies typically better than 20
arcsec, allowing immediate identification of the most probable optical
counterparts. Only 3% of all extragalactic HI sources and fewer than 1% of
detections with M(HI) > 10**9.5 Msun cannot be identified with a stellar
component. First ALFALFA results already suggest, in agreement with previous
studies, that there does not appear to be a cosmologically significant
population of optically dark but HI rich galaxies. ALFALFA promises a wealthy
dataset for the exploration of many issues in near-field cosmology and galaxy
evolution studies, setting the stage for their extension to higher redshifts
with the Square Kilometer Array (SKA).
