Radio observations of colliding winds in massive stars
  This brief review describes radio observations of colliding winds in massive
stars starting with the first direct observational support for the
colliding-wind model advanced in the early 1990's to explain non-thermal radio
and thermal X-ray emission in some massive stars. Studies of the well-studied
and highly-eccentric WR+O star system WR140 are described along with recent
observations of O-star systems. Also discussed is the binary nature of almost
all massive stars that exhibit non-thermal behavior and some strategies for
finding new systems.
