Massive Young Stellar Clusters in the Milky Way

Compact young open clusters with very high masses (M-cl greater than or similar to 10(5) M-circle dot) have been observed in many galaxies, and their connection to globular clusters is a matter of discussion. However, until very recently, no clusters with masses M-cl greater than or similar to 10(4) M-circle dot were known in the Milky Way. Their absence was considered a natural consequence of the mild star formation rate in the Milky Way. The development of new infrared observational techniques has completely changed our perception. At present, almost a dozen young massive clusters are known in the Milky Way, and there are reasons to believe that many more wait to be found. In this paper, I briefly review our knowledge of some of these objects: the extended star-forming region Cygnus OB2, the compact young massive cluster Westerlund I, currently believed to be the most massive young cluster in the Galaxy, and the new massive clusters hosting a large population of red supergiants found at the base of the Scutum Arm.