The creation of a lexicon in the manuscript culture of the Greek Middle Ages was a complex and difficult enterprise. It required access to different manuscript sources and to writing materials in which the selected information could be copied and structured. To illustrate this practice, some features of the manuscript Vatican City, BAV, Vaticanus Barberinianus gr. 70 (eleventh century CE?) transmitting the original of the so-called Etymologicum Gudianum will be investigated.