  In the present review we discuss the past and present status of the
interacting OB-type binary frequency. We critically examine the popular idea
that Be-stars and supergiant sgB[e] stars are binary evolutionary products. The
effects of rotation on stellar evolution in general, stellar population studies
in particular, and the link with binaries will be evaluated. Finally a
discussion is presented of massive double compact star binary mergers as
possible major sites of chemical enrichment of r-process elements and as the
origin of recent aLIGO GW events.
