The physics and modes of star cluster formation: observations
  Stellar clusters are born in cold and dusty molecular clouds and the youngest
clusters are embedded to various degrees in dusty dark molecular material. Such
embedded clusters can be considered protocluster systems. The most deeply
buried examples are so heavily obscured by dust that they are only visible at
infrared wavelengths. These embedded protoclusters constitute the nearest
laboratories for direct astronomical investigation of the physical processes of
cluster formation and early evolution. I review the present state of empirical
knowledge concerning embedded cluster systems and discuss the implications for
understanding their formation and subsequent evolution to produce bound stellar
clusters.
