[en] In binary systems consisting of two massive stars, the interaction of the powerful stellar winds of the two components produces signatures over a broad range of wavelengths. Many observational and theoretical studies of this phenomenon have been performed over the last two decades. In very close massive binary systems, mass exchange due to Roche lobe overflow can also occur and the signatures of the two phenomena are sometimes hard to distinguish. In this review, I discuss some recent developments in the study of both phenomena.
