  We investigate the physical and mathematical structure of a new class of
geometric transitions proposed by Aganagic and Vafa. The distinctive aspect of
these transitions is the presence of open string instanton corrections to
Chern-Simons theory. We find a precise match between open and closed string
topological amplitudes applying a beautiful idea proposed by Witten some time
ago. The closed string amplitudes are reproduced from an open string
perspective as a result of a fascinating interplay of enumerative techniques
and Chern-Simons computations.
