We present a systematic study of light transmission through individual nanoscale apertures (rectangular slits and circular holes) etched in a 300-nm-thick silver film. Transmission spectra were obtained as functions of aperture shape and size, as well as the wavelength and polarization state of the normally incident light beam. By varying the wavelength of the incident light in the 550-750 nm range and the characteristic dimensions of the apertures from ∼100 nm to 10 μm, a universal behavior of light transmission is revealed. The role of incident polarization and aperture dimensions is investigated in detail, and a clear transition from the geometric regime of light transmission (large apertures) to the subwavelength regime is demonstrated experimentally. A quantitative analysis of the extinction coefficient is reported for rectangular slits, demonstrating that they can act as efficient linear polarizers with extinction ratios >100∶1. Finally, a method to convert far-field to near-field data is developed for circular apertures, revealing the contribution of surface plasmon polaritons to the decrease in light transmission for apertures below the cutoff condition.