Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Hubert F.M. Goenner,
"On the History of Unified Field Theories",
Living Rev. Relativity 7, (2004), 2. URL (accessed <date>):
The date given as <date> then uniquely identifies the version of the article you are referring to.