Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Ingo Müller,
"Speeds of Propagation in Classical and Relativistic Extended Thermodynamics",
Living Rev. Relativity 2, (1999), 1. URL (cited on <date>):
http://www.livingreviews.org/lrr-1999-1
The date given as <date> then uniquely identifies the version of the article you are referring to.