title: Optical orbital angular momentum.
abstract: We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next.This article is part of the themed issue 'Optical orbital angular momentum'.
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK stephen.barnett@glasgow.ac.uk.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Barnett
authors.affiliation: Department of Physics, University of York, Heslington, York YO10 5DD, UK.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Babiker
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Miles J
authors.initials: MJ
authors.lastname: Padgett
keywords: optics; orbital angular momentum; spin