W43 is one of the most active star-forming regions in the Galaxy. Its position in the Galactic plane and its radial velocity places it at the junction point of the Galactic long bar and the Scutum spiral arm at 5.5 kpc distance to the Sun. It contains two of the largest cloud groups of the first Galactic quadrant (W43 Main and South) with a total mass of ~6×10⁶ M_⊙. W43 Main is heated by a cluster of Wolf-Rayet and OB stars (~3.5×10⁶ L_⊙) and is considered to be a Galactic mini-starburst region since it is undergoing a remarkably efficient episode of high-mass star-formation (~15 high-mass protoclusters and a star-formation efficiency (SFE) of ~0.1 M_⊙ yr^-1). The formation of the cluster was likely supported by the expansion of an older H II region to the south that triggered the formation and gravitational collapse of the molecular cloud that evolved into W43. Subsequently UV radiation from the central O+WR cluster compressed the parent cloud towards both low- and high Galactic longitudes, triggering the formation of additional massive stars. Its mini star burst activity is continuously fueled by converging flows, owing to its position at the meeting point of the ScutumCentaurus (or Scutum-Crux) Galactic arm and the bar.