The diffraction of a plane electromagnetic wave by an infinitely long, unidirectionally conducting strip is formulated as a Wiener–Hopf integral equation and is solved asymptotically for a wide strip by transform techniques. In addition to the diffracted fields produced by a perfectly conducting strip, surface-wave excitation and scattering at the edges and interaction between the ends of the lines of conductivity appear in the solution. These effects are illustrated by numerical results of the scattering cross section at normal incidence for various directions of conductivity.