  We have carefully selected a sample of 60 galaxies that reside in the deepest
underdensities of geometrically identified voids within the SDSS. HI imaging of
55 galaxies with the WSRT reveals morphological and kinematic signatures of
ongoing interactions and gas accretion. We probe a total volume of 485 Mpc^3
within the voids, with an angular resolution of 8 kpc at an average distance of
85 Mpc. We reach column density sensitivities of 5 x 10^19 cm^-2, corresponding
to an HI mass limit of 3 x 10^8 M_sun. We detect HI in 41 galaxies, with total
masses ranging from 1.7 x 10^8 to 5.5 x 10^9 M_sun. The upper limits on the 14
non-detections are not inconsistent with their luminosities, given their
expected HI mass to light ratios. We find that the void galaxies are generally
gas rich, low luminosity, blue disk galaxies, with optical and HI properties
that are not unusual for their luminosity and morphology. The sample spans a
range of absolute magnitudes (-16.1 > M_r > -20.4) and colors (0.06 < g-r <
0.87), and includes disk and irregular galaxies. We also identify three as
early type galaxies, all of which are not detected in HI. All galaxies have
stellar masses less than 3 x 10^10 M_sun, and many have kinematic and
morphological signs of ongoing gas accretion, suggesting that the void galaxy
population is still in the process of assembling. The small scale clustering in
the void, within 600 kpc and 200 km/s, is similar to that in higher density
regions, and we identify 18 HI rich neighboring galaxies in the voids. Most are
within 100 kpc and 100 km/s of the targeted galaxy, and we find no significant
population of HI rich low luminosity galaxies filling the voids, contrary to
what is predicted by simulations.
