The book shows lines of development in Roman law relating to the legal institution of conditional donation, which leads to consequences for thinking about the law of enrichment, especially in the form of the condictio ob rem with a view to a general understanding of the dationes ob rem. The author examines the Roman legal aspects of a donation, which is characterized by the fact that the donor also imposes a certain action or omission on the recipient. Because the acquisition of liberalitas is linked to an obligation on the part of the recipient, a number of questions arise that have not lost their topicality in modern civil law: Is the benefit associated with an obligation on the part of the recipient still a gift or already a mixed one, even paid business? What is the claim of the donor or the third party entitled to conditions if the condition is not met? What is the difference between a conditional donation and a negotium mixtum cum donatione? And last but not least, what is the relationship between non-compliance with the condition and ingratitude on the part of the recipient?