The Interstellar Extinction Toward the Milky Way Bulge with Planetary
  Nebulae, Red Clump, and RR Lyrae stars
  I review the literature covering the issue of interstellar extinction toward
the Milky Way bulge, with emphasis placed on findings from planetary nebulae,
RR Lyrae, and red clump stars. I also report on observations from HI gas and
globular clusters. I show that there has been substantial progress in this
field in recent decades, most particularly from red clump stars. The spatial
coverage of extinction maps has increased by a factor $\sim 100 \times$ in the
past twenty years, and the total-to-selective extinction ratios reported have
shifted by $\sim$20-25\%, indicative of the improved accuracy and separately,
of a steeper-than-standard extinction curve. Problems remain in modelling
differential extinction, explaining anomalies involving the planetary nebulae,
and understanding the difference between bulge extinction coefficients and
"standard" literature values.
