  The solar nebula contained a number of short-lived radionuclides (SLRs) with
half-lives of tens of Myr or less, comparable to the timescales for formation
of protostars and protoplanetary disks. Therefore, determining the origins of
SLRs would provide insights into star formation and the Sun's astrophysical
birth environment. In this chapter, we review how isotopic studies of
meteorites reveal the existence and abundances of these now-extinct
radionuclides; and the evidence that the SLR ${}^{10}{\rm Be}$, which uniquely
among the SLRs is not produced during typical stellar nucleosynthesis, was
distributed homogeneously in the solar nebula. We review the evidence that the
SLRs ${}^{26}{\rm Al}$, ${}^{53}{\rm Mn}$, and ${}^{182}{\rm Hf}$, and other
radionuclides, were also homogeneously distributed and can be used to date
events during the Solar System's planet-forming epoch. The homogeneity of the
SLRs, especially ${}^{10}{\rm Be}$, strongly suggests they were all inherited
from the Sun's molecular cloud, and that production by irradiation within the
solar nebula was very limited, except for ${}^{36}{\rm Cl}$. We review
astrophysical models for the origin of ${}^{10}{\rm Be}$, showing that it
requires that the Sun formed in a spiral arm of the Galaxy with higher star
formation rate than the Galaxy-wide average. Likewise, we review the
astrophysical models for the origins of the other SLRs and show that they
likely arose from contamination of the Sun's molecular cloud by massive stars
over tens of Myr, most likely dominated by ejecta from Wolf-Rayet stars. The
other SLRs also demand formation of the Sun in a spiral arm of the Galaxy with
a star formation rate as high as demanded by the Solar System initial
${}^{10}{\rm Be}$ abundance. We discuss the astrophysical implications, and
suggest further tests of these models and future directions for the field.
