title: Introduction.
abstract: Since its first report in 1998 by Ebbesen et al., the extraordinary transmission of light through an array of subwavelength apertures in an otherwise opaque metal film has resulted in equally-extraordinary activity in this and related phenomena in nanophotonics. In fact, as of the publication of this Focus Issue, the 1998 Ebbesen Nature paper has been referenced nearly 300 times. Given this level of activity, it comes as no surprise that multiple explanations exist as to the origin of extraordinary transmission through periodic arrays of subwavelength apertures (as evidenced by contributions in this Focus Issue). Even as the physical mechanisms are being investigated, we are witnessing the emergence of significant applications of these sub-wavelength structured surfaces, from their use as simple passive components to their use in electro-luminescent devices and biological sensors.
authors.forename: Steve
authors.initials: S
authors.lastname: Blair
authors.forename: Ajay
authors.initials: A
authors.lastname: Nahata