Since 1974 the Central Archive of Historical Records in Warsaw has been in possession of a source called 'Book of accounts of the court of King John III Sobieski. Kitchen expenses'. The book, which is actually a register of the upkeep of the royal kitchen, records exactly what food was served by the royal kitchen between the 5th of August 1695 and the 31st of January 1696 (with a few gaps resulting from pages having been torn out). The book includes daily notes on the food provided for the table of the king, of the queen, of their sons, of the guests, of the courtiers and of the servants. The author of the book is unknown, but he must have been a person employed at the royal court (a steward, a cook or an assistant to one of those). The notes are very systematically structured, since they list the victuals served to the particular tables in the same order under subsequent dates. They reveal what amounts and kinds of food (meat, fish, sweets) were available to the royal family and its entourage for lunch and dinner. Since the notes cover a relatively long period, it is possible to discover differences between the meals served on weekdays, holidays and fast days. Furthermore, the source allows to reconstruct with much precision the itinerary of the royal court, as the place of serving every meal is also indicated. The record is of great value, since it shows the differences in the quantity and quality of food provided for the different groups in the court, ranging from the royal family to the servants of the royal guests. The book can also be used to draw some conclusions about the entourage of King John III in the last year of his life. The notes from the royal kitchen indicate that it prepared meals for a relatively stable number of people (between ten and twenty; several dozen if larger groups, e.g. pages, are taken into consideration). A detailed analysis of this source may reveal the expenses incurred by the privy purse to feed the royal family and court, as well as the dietary habits of this small community. A comparison of such data with the data concerning the kitchen expenses of John III's predecessors and successors on the Polish throne, and of other European courts, may extend our understanding of the costs and functioning of royal courts.