The HOBYS Key Program: When Herschel links high-mass star formation to cloud structure

International audience; With its unprecedented spatial resolution and high sensitivity in the far-infrared to submillimetre regime, {Herschel} is revolutionizing our understanding of star formation. The HOBYS key program is an {Herschel} mapping survey dedicated to the formation of OB-type stars (Motte, Zavagno, Bontemps et al. 2010; see {http://hobys-herschel.cea.fr}. HOBYS aims at 1) discovering and characterizing the progenitors of high-mass stars, 2) making the link between the latters and their filamentary background, and 3) assessing the importance of triggering. Among the HOBYS highlights is the discovery of ''mini-starburst ridges" defined as high-density dominating filaments supersonically contracting and efficiently forming clusters of high-mass stars. Their existence is predicted by dynamical models of cloud formation such as converging flows and is favoring a (high-mass) star formation scenario involving gas flows and global infall. The present star formation rate measured within these ridges is high enough for these 1-10 pc^2 regions to be considered as miniature and instantaneous models of extragalactic starbursts.