The Geniza Documents is the name of a collection of merchant records stored in sacred storage room (known as a geniza) in theBen Ezra Jewish synagogue in Old Cairo. The documents were discovered by Dr. Solomon Schecter and Charles Taylor of Cambridge University. Altogether there were about 193,000 manuscripts. You can explore more about these documents online through the websites of the The Taylor-Schechter Cairo Genizah Collection at Cambridge University Library. These documents contain key commercial records of the 11th – 12th century and in later centuries among the minority Jewish community in Cairo and throughout the Eastern Mediterranean and make up a valuable resource into understanding some of the movement and trade in goods during this period.
The interconnections around the Mediterranean in this period can be seen in the following abstract of this document
BL OR 5544.1
As the records are mostly related to marriage, probate and commercial documents they are less useful for in-depth study in areas of culture and science, although many observations on cultural and social matters may be gleaned from them. As a result they tend to be used more for economic or business history. Most of the documents are fragments and although written mostly in Hebrew, are also made up of Arabic and Aramaic texts. A second digital archive of a portion of these records is available for browsing at Princeton University’s Geniza Project database.
Here are some links from the Princeton University database to helpful articles that give you a sense of how to use these records to frame historical interpretations.