In this article, we investigate the glass transition in polystyrene melts and free-standing ultra-thin films by means of large-scale computer simulations. The transition temperatures are obtained from static (density) and dynamic (diffusion and orientational relaxation) measurements. As it turns out, the glass transition temperature of a 3 nm thin film is similar to 60 degrees K lower than that of the bulk. Local orientational mobility of the phenyl bonds is studied with the help of Legendre polynomials of the second-order P-2(t). The alpha and beta relaxation times are obtained from the spectral density of P-2(t). Our simulations reveal that interfaces affect alpha and beta-relaxation processes differently. The beta relaxation rate is faster in the center of the film than near a free surface; for the a relaxation rate, an opposite trend is observed. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1160-1167, 2010