A High-Mass X-ray Binary (HMXB) is a binary star system consisting of a massive star (>10M⊙, usually O/B star) dominating the emission of optical light and a X-ray emitting compact object being a neutron star or a black hole. In those systems, the massive star looses large amounts of its mass via radiation-driven mass loss or ”stellar wind” (see Fig. 1). Some of the wind is captured by the compact object. As it is accreted onto the compact object, it produces X-rays. HMXBs are building blocks of star clusters and galaxies as they significantly influence the surrounding medium via gas outflow and ionising radiation.