Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Hari K. Kunduri and James Lucietti,
"Classification of Near-Horizon Geometries of Extremal Black Holes",
Living Rev. Relativity 16, (2013), 8. URL (accessed <date>):
The date given as <date> then uniquely identifies the version of the article you are referring to.