Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Slava G. Turyshev and Viktor T. Toth,
"The Pioneer Anomaly",
Living Rev. Relativity 13, (2010), 4. URL (accessed <date>):
The date given as <date> then uniquely identifies the version of the article you are referring to.