  I present results on the interstellar medium towards the O stars observed in
five optical spectroscopic surveys: GOSSS, OWN, IACOB, NoMaDS, and
CAF\'E-BEANS. I have measured both the amount [$E(4405-5495)$] and type
[$R_{5495}$] of extinction towards several hundreds of Galactic O stars and
verified that the Ma\'iz Apell\'aniz et al. (2014) family of extinction laws
provides a significantly better fit to optical+NIR Galactic extinction than
either the Cardelli et al. (1989) or the Fitzpatrick (1999) families.
$R_{5495}$ values are concentrated between 3.0 and 3.5 but for low values of
$E(4405-5495)$ there is a significant population with larger $R_{5495}$
associated with H II regions. I have also measured different DIBs and I have
found that $W$(5797)/$W$(5780) is anticorrelated with $R_{5495}$, a sign that
extreme $\zeta$ clouds are characterized not only by low ionization
environments (as opposed to $\sigma$ clouds) but also by having a larger
fraction of small dust grains. The equivalent width of the "Gaia DIB" (8621
\AA) is strongly correlated with $E(4405-5495)$, as expected, and its behavior
appears to be more $\sigma$-like than $\zeta$-like. We have also started
analyzing some individual sightlines in detail.

Astrophysics of Galaxies;Solar and Stellar Astrophysics