  The local luminosity function at 25 $\mu$m provides the basis for
interpreting the results of deep mid-infrared surveys planned or in progress
with space astrophysics missions including ISO, WIRE and SIRTF. We have
selected a sample of 1458 galaxies from the IRAS Faint Source Survey with a
flux density limit of 250 mJy at 25 $\mu$m. The local luminosity function is
derived using both parametric and non-parametric maximum-likelihood techniques,
and the classical $1/V_{max}$ estimator. Comparison of these results shows that
the $1/V_{max}$ estimate of the luminosity function is significantly affected
by the Local Supercluster. A maximum-likelihood fit to the radial density shows
no systematic increase that would be caused by density evolution of the galaxy
population. The density fit is used to correct the $1/V_{max}$ estimate. We
also demonstrate the high quality and completeness of our sample by a variety
of methods. The luminosity function derived from this sample is compared to
previously published estimates, showing the prior estimates to have been
strongly affected by the Local Supercluster. Our new luminosity function leads
to lower estimates of mid-infrared backgrounds and number counts.
