Observational aspects of hot star winds The considerable radiative pressure of massive hot stars is a very efficient engine for the ejection of stellar winds. In addition, hot stars are often also fast rotators. In this case, their flattened photosphere result in overheated polar caps through the Von Zeipel effect, and a low effective gravity at the equator. Mass loss occurs from both the poles (fast stellar wind) and the equator (slower wind). The geometry of the envelopes of fast rotating stars is therefore often assumed to be formed by a hot polar wind and a disk around the stellar equator. As most massive stars are members of binary or multiple systems, stellar interactions also play a fundamental role. These phenomena have several observable consequences. For instance, Be stars show evidence of mass loss and circumstellar envelopes from UV resonance lines, near-IR excesses, and the presence of episodic hydrogen emission lines. In this short review, I will present recent observational results from long-baseline interferometry and other techniques.