  This review addresses the current observational status of the Baldwin Effect
(BE), an empirical anti-correlation between emission line equivalent width and
source luminosity for active galactic nuclei. We provide a brief history of the
BE, and discuss selection effects and analysis methods relevant to its study.
Existing research points to a number of detailed patterns in the BE, involving
emission-line profiles and ionization, luminosity range, and radio properties,
that provide clues to the underlying physics driving the correlation. We
present a comparative analysis of the "global" BE for AGN ensembles and the
"intrinsic" BE seen in variable Seyfert nuclei, and also examine similarities
and differences in BEs reported in the optical/UV and X-ray bandpasses. A
summary of measurements for quasars at high redshift (z > 4) suggests that the
BE persists among these extreme objects. We close with an assessment of current
needs and future opportunities for strengthening the observational picture of
the BE.
