The star formation rate (SFR) in galaxies, as measured by optical, UV and far-infrared observations, appears to increase by an order of magnitude over the redshift interval of z=0 to z≈1. However, little accurate information about the co-evolution of neutral hydrogen is available. Measurements are limited to sparse and model-dependent observations of damped Lyman-α systems at high redshifts or to observations of 21cm radio emission line at very low redshift. However, the unique sensitivity of the Arecibo telescope can be used to directly detect 21-cm HI emissions from galaxies at cosmological distances. Previous detections have involved optically pre-selected galaxies and are therefore biased in their selection criteria. Here we present results from the ongoing Arecibo Ultra Deep Survey (AUDS) which is a blind 21-cm survey with the Arecibo L-band Feed Array (ALFA). We use data from AUDS to accurately derive the HI mass function and constrain the cosmic HI density ΩHI at redshifts greater than zero for the ﬁrst time.