  We measure C III] 1907,1909 A emission lines in eleven
gravitationally--lensed star-forming galaxies at z~1.6--3, finding much lower
equivalent widths than previously reported for fainter lensed galaxies (Stark
et al. 2014). While it is not yet clear what causes some galaxies to be strong
C III] emitters, CIII] emission is not a universal property of distant
star-forming galaxies. We also examine C III] emission in 46 star-forming
galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS
on HST, and IUE. Twenty percent of these local galaxies show strong C III]
emission, with equivalent widths <-5 A. Three nearby galaxies show C III]
emission equivalent widths as large as the most extreme emitters yet observed
in the distant universe; all three are Wolf-Rayet galaxies. At all redshifts,
strong C III] emission may pick out low-metallicity galaxies experiencing
intense bursts of star formation. Such local C III] emitters may shed light on
the conditions of star formation in certain extreme high-redshift galaxies.
