The structure and dynamics of luminescent excitons in tetracene thin films and nanoaggregates are investigated using time-resolved spectroscopy and theoretical calculations. The orientation of tetracene's transition dipole moment along its short molecular axis leads to properties qualitatively different from those observed in aggregates of phenylene-vinylene and thiophene oligomers, despite similar crystal structures. The spectral shape, temperature dependence, and radiative lifetime are consistent with a short-lived superradiant exciton delocalized over approximately 10 tetracene molecules.