  A detailed study spanning approximately a year has been conducted on the Type
Ib supernova 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a
comprehensive set of multi-band (w2m2w1u'g'r'i'UBVYJHKs) light curves and
optical spectroscopy is presented. A virtually complete bolometric light curve
is derived, from which we infer a (56)Ni-mass of 0.06 M_sun. The early spectrum
strongly resembles SN 2005bf and exhibits high-velocity features of CaII and
H_alpha; during late epochs the spectrum shows evidence of a ejecta-wind
interaction. Nebular emission lines have similar widths and exhibit profiles
that indicate a lack of major asymmetry in the ejecta. Late phase spectra are
modeled with a non-LTE code, from which we find (56)Ni, O and total-ejecta
masses (excluding He) to be 0.06, 0.2 and 0.42 M_sun, respectively, below 4,500
km/s. The (56)Ni mass confirms results obtained from the bolometric light
curve. The oxygen abundance suggests the progenitor was most likely a ~3.3
M_sun He core star that evolved from a zero-age-main-sequence mass of 10-13
M_sun. The explosion energy is determined to be ~10^50 erg, and the mass-loss
rate of the progenitor is constrained from X-ray and radio observations to be
<~10^-6 M_sun/yr. SN 2007Y is among the least energetic normal Type Ib
supernovae ever studied.
