  We present the luminosity function of 90um selected galaxies from the
European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities
are in the range 10^9 < h_65^-2 L/Lsun < 10^12, i.e. non-ultraluminous. From
our sample of 37 reliably detected galaxies in the ELAIS S1 region from the
Efstathiou et al. (2000) S_90 >= 100mJy database, we found optical, 15um or
1.4GHz identifications for 24 (65%). We have obtained 2dF and UK Schmidt FLAIR
spectroscopy of 89% of IDs to rigid multivariate flux limits. We construct a
luminosity function assuming (a) our spectroscopic subset is an unbiased sparse
sample, and (b) there are no galaxies which would not be represented in our
spectroscopic sample at {\it any} redshift. We argue that we can be confident
of both assumptions. We find the luminosity function is well-described by the
local 100um luminosity function of Rowan-Robinson, Helou & Walker (1987). {\it
Assuming} this local normalisation, we derive luminosity evolution of
(1+z)^{2.45\pm0.85} (95% confidence). We argue that star formation dominates
the bolometric luminosities of these galaxies and we derive comoving star
formation rates in broad agreement with the Flores et al. (1999) and
Rowan-Robinson et al. (1997) mid-IR-based estimates.
