Owing to the fact that a Living Reviews article may evolve over time, we recommend to cite the article as follows:

Jean-Yves Vinet ,
"On Special Optical Modes and Thermal Issues in Advanced Gravitational Wave Interferometric Detectors",
Living Rev. Relativity 12,  (2009),  5. URL (cited on <date>):
http://www.livingreviews.org/lrr-2009-5

The date given as <date> then uniquely identifies the version of the article
you are referring to.