  We present 3-dimensional kinematical observations of the massive OB
association Cygnus OB2 to identify the mechanisms responsible for disrupting
young star clusters. The picture revealed by these observations is of a
highly-substructured, dynamically unmixed OB association that does not exhibit
the position-velocity correlations predicted by the theories of infant
mortality or tidal stripping. These observations would appear to support a
picture of hierarchical star formation.
