The coupling of light to surface plasmons through periodic subwavelength metallic structures could strongly modify the optical properties of a metal film. We demonstrate that the optical transmission through an array of subwavelength slits is as high as 80% at resonance, even though the width of each slit is almost 10 times smaller than the wavelength and the slits occupy only 25% of the area of the metal. Numerical calculations suggest that the field intensity is strongly enhanced near the metal surface. The field enhancement could be used for generating nonlinear optical effects and for high sensitivity detection of nanomechanical displacement. © 2005 Lucent Technologies Inc.