Scaling relations of stellar mass (Mstar), star-formation rate (SFR), and
metallicity (O/H) provide strong clues for how galaxies evolve over cosmic
time.  This talk will explore correlations of stellar mass, SFR, and O/H from
redshift z=0 to z<=3.5 based on a sample of ~1000 star-forming galaxies with
metallicity measurements spanning almost a factor of 100.  Results suggest that
specific SFR and O/H mutually evolve in a way that makes the scaling relations
of Mstar, O/H, and SFR redshift invariant, at least over the redshift range of
the sample.  To gain insight into a physical understanding of the trends,
predictions of recent theoretical models will also be discussed. Comparing
model predictions with data indicates that the properties of gas outflow
through galactic winds and gas accretion do not change significantly with
cosmic time, but rather that the redshift invariance is a consequence of other
changes in the way galaxies evolve.