The Duchy of Frýdlant, this “state within a state”, as characterized by many authors, existed only for a very short period of time. The fief estates, which were acquired by the imperial military leader Albrecht von Wallenstein (Valdštejn) in the sale following the Battle of White Mountain, were first declared a principality in 1624 and then a duchy in 1627. Immediately after Wallenstein's assassination in 1634, this remarkable constitutional unit was immediately liquidated. Wallenstein kept most of the acquired estates under his direct control, and they thus became chamber ducal estates (this was especially true for all larger, economically strong towns). He left only a relatively small part of his property to the institutions of the Catholic Church – logically, although he provided them with political and property support, in the latter respect he certainly did not dazzle with excessive generosity. On the other hand, he left large estates to various persons (his relatives, subordinate officers, officials, in some cases the original pre-White Mountain owners, etc.), who took them over from him as a Frydlant fief (de iure actually sub-fief, as Wallenstein himself was a vassal of the emperor who was the Czech king). Some of these people received the property as a gift (“Donatio”) as a sign of Wallenstein's generosity. In most cases, however, it was a standard property transaction, where the acquirers paid a more or less adequate amount of money for the fief estate, or their receivables from the Frýdlant landowner were offset. The legal title of the transfer of possession thus became the standard purchase (“Erblehenkauf”), recorded in a contract approved, sealed and signed by both parties. Copies of these contracts are concentrated in the manuscript sign. B 16, stored in the National Archives in Prague, other originals and copies of individual documents of this type can be recorded in other archives. This study is devoted to their content analysis. Purchase contracts for Frýdlant fief estates represent a set of documents, the significance of which can be seen on at least four levels. From the most general point of view, they contribute to the knowledge of early modern legal culture and legal language (although German, not Czech). Secondly, they are evidence of the administrative practice of the court office of the Duchy of Frýdlant, which prepared these documents. They are also a contribution to the history of fief law in the Czech lands. Finally, they provide a number of specific information about individual fief estates, and thus also about the regional history of northeastern Bohemia, where Wallenstein's “terra felix” was located. The surviving contracts relate to more than forty larger and smaller estates, which fell into the hands of the vassals in the short days of Wallenstein’s rule over this region. The court office of the Duchy of Frýdlant, on whose premises the contracts were created, was a relatively advanced bureaucratic body with several lawyers – the former prosecutor Jan Jezber of Kolivá Hora had probably the greatest reputation, who himself bought the Choteč fief estate in 1624. Štěpán Ilgen from Ilgenau, a native of Leipzig, reached the significant position of Frýdlant Chancellor. Many office councilors were also graduates of law education. However, it is very interesting that the set of surviving contracts is largely characterized by its variability. Although a more or less uniform structure was followed (dating, definition of the contracting parties, and the subject of the contract, determination of the price and the method of payment, set of rights reserved to the landlord, confirmation of will and corroboration), contracts offer various and in some cases significantly different specific solutions. On the other hand, different wording did not always mean a difference in content. For example, the extent of the landlord reservations, which Wallenstein reserved in the treaties as chief lord of the Duchy of Frýdlant and among which brewing played the most important role, apparently had a standard scope, regardless of the specific diction. Purchase contracts related to Frýdlant fief estates represent only one type of documents framing the development of this extremely interesting state law unit. The study of others and, in the future, comprehensive elaboration of the history of the Frýdlant estate, or of the entire duchy, remain urgent challenges for further legal historical research.