The concept of mukâtaa is used to express practices that have different legal consequences in foundation law, as in Ottoman financial law. In this study, the focus is mainly on the practice of mukataa, which means renting the foundation land to anyone who wants to build a building or plant a tree, with the right of decision and ownership of it. The foundations of the mukâtaa practice date back to before the Ottoman Empire, and the Ottomans further developed this practice, which they inherited, with some arrangements and used it for centuries. However, Ottoman lawyers, who saw that the mukâtaa practice caused the abuse of foundations over time, did not insist on this practice, on the contrary, they developed the more advantageous icâreteyn practice for foundations. This shows that mukataa paved the way for the practice of icareteyn. In this book, the historical background, nature, different practices, conditions, legal principles and rights of the mukataa contract in the 16th and 17th centuries have been tried to be revealed, especially based on fatwa journals and sharia registers.