Eighteen years ago. Fredrickson et al, [Macromolecules 1992, 25, 2882-2889] predicted that a molten polymer brush possesses a shear modulus that would cause its surface structure to deviate from a liquid. Their prediction, though broadly used, has been largely unchecked. Here, we present experimental data on polystyrene brushes that validate Fredrickson et al.'s prediction. We also present data obtained by following the time evolution of the surface structure of an entangled brush, which shows that the equilibrium shear modulus is established prior to the onset of the terminal flow regime. This suggests that the dynamics of entangled polymer brush is not governed by chain reptation motions, contrary to a previous presumption.