Received; accepted

We present 18 spectra, obtained with the Keck 10m telescope, of faint eld galaxies (19 < I < 22, 0.2 < z < 0.84) previously imaged by HST's WFPC2. Though small, our sample appears to be representative of eld spirals with a magnitude{limit of I 22. Combining the results from the spectral and imaging data, we have derived various quantitative parameters for the galaxies, including colors, inclinations, emission line equivalent widths, redshifts, luminosities, internal velocity information and physical scale lengths. In particular, disk scale lengths (with sizes ranging from 1{5 kpc) have been measured from ts to the surface brightness proles. We have also measured internal velocities with a rest frame resolution of = 55 to 80 km s 1 by tting to the emission lines. The luminosity{disk size and luminosity{internal velocity (Tully{Fisher) relations for our moderate redshift galaxies are similar to the scaling relations seen for local galaxies, albeit with a modest brightening of 1 magnitude. The one bulge{dominated galaxy in our sample (at z = 0.324) has a relatively blue color, reveals weak emission lines and is 0.5 magnitude brighter in the rest frame than expected for a passive local elliptical. Our data suggest that galaxies at about half the age of the Universe have undergone mild luminosity evolution to the present epoch, but are otherwise quantitatively similar to galaxies seen locally