  Canonical grids of stellar evolutionary sequences have been computed for the
helium mass-fraction abundances $Y = 0.25$, $0.29$, and $0.33$, and for iron
abundances that vary from $-2.4$ to $+0.4$ (in 0.2 dex increments) when
[$\alpha$/Fe] $= +0.4$, or for the ranges $-2.0 \le$ [Fe/H] $\le +0.6$, $-1.8
\le$ [Fe/H] $\le +0.6$ when [$\alpha$/Fe] $= 0.0$ and $-0.4$, respectively. The
grids, which consist of tracks for masses from $0.12 {{\cal M}_\odot}$ to
$1.1$-$1.5 {{\cal M}_\odot}$ (depending on the metallicity) are based on
up-to-date physics, including the gravitational settling of helium (but not
metals diffusion). Interpolation software is provided to generate isochrones
for arbitrary ages between $\approx 5$ and $15$ Gyr and any values of $Y$,
[$\alpha$/Fe], and [Fe/H] within the aforementioned ranges. Comparisons of
isochrones with published color-magnitude diagrams (CMDs) for the open clusters
M67 ([Fe/H] $\approx 0.0$) and NGC 6791 ([Fe/H] $\approx 0.3$) and for four of
the metal-poor globular clusters (47 Tuc, M3, M5, and M92) indicate that the
models for the observed metallicities do a reasonably good job of reproducing
the locations and slopes of the cluster main sequences and giant branches. The
same conclusion is reached from a consideration of plots of nearby subdwarfs
that have accurate Hipparcos parallaxes and metallicities in the range $-2.0
\le$ [Fe/H] $\le -1.0$ on various CMDs and on the ($\log T_{\rm
eff},\,M_V$)-diagram. A relatively hot temperature scale similar to that
derived in recent calibrations of the infrared flux method is favored by both
the isochrones and the adopted color transformations, which are based on the
latest MARCS model atmospheres.
