  The optical regime is historically the best-studied wavelenght range. Gas
ionized by massive stars produces optical emission lines that have been used to
derive indicators of star-formation rate, metallicity, dust reddening, and the
ionization conditions of the interstellar medium. Absorptions lines have been
used to measure velocity dispersions, and the 4000 A break has been shown to be
a useful indicator of the mean age of stellar populations. I briefly summarize
some recent work done on, specifically, star formation rate indicators, in view
of their importance for understanding star-forming galaxies at high redshift.
