One of the few historical records kept in the Shire, Yellowskin was a book of extraordinary age, said to contain entries dating back some nine hundred years before the War of the Ring. This would place the first entries in the book at about III 2100 (or some five hundred years after the founding of the Shire). It contained chronicles of the Took family, including not only marriages, births and deaths, but also legal details and references to important events in the Shire as a whole. Yellowskin became a source for much of the historical information, especially about the Tooks, to find its way into the Red Book of Westmarch.

The name 'Yellowskin' presumably derives from the aged and decayed condition of the book, suggesting that the records of the Tooks were recorded on vellum, or some other form of parchment. These materials were made from animal skins, and so 'Yellowskin' would be a literal description of the nature of the book.