It is crucial to better understand the winds from massive stars. Not only does their mass loss affect their own evolution but it contributes an amount of energy and momentum to the ISM capable of affecting the chemical and dynamical evolution of their environments. Hot star binaries offer an opportunity to learn more. Colliding winds in such systems might be expected to lead to a bow shock which wraps around the star with the weaker wind. As material flows along the shock, it may give rise to extra line emission. Variations in these emission features may allow the characteristics of the shock region to be deduced thus providing a wealth of information about the winds.