Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Steven Carlip,
"Quantum Gravity in 2+1 Dimensions: The Case of a Closed Universe",
Living Rev. Relativity 8, (2005), 1. URL (accessed <date>):
http://www.livingreviews.org/lrr-2005-1
The date given as <date> then uniquely identifies the version of the article you are referring to.