  This paper presents a brief survey of the evolution of knowledge about
diffraction gratings. After recalling some basic facts, historically and
physically, we introduce the concept of Wood anomalies. Next, we present some
recent works in order to introduce the role of bounded modes in transmission
gratings. The consequences of these recent results are then introduced. This
paper is a secondary publication, published in Europhysics News (EPN 38, 3
(2007) 27-31). In the present version, some additional notes have been added
with related references.
