This book is the first comprehensive study on the general theory of obligations in Qatari civil law, addressing both voluntary and non-voluntary sources of obligation. The Qatari legislator has structured the sources of obligation in Articles (64) to (240) of the Qatari Civil Code No. (22) of 2004. The book presents an applied comparative analysis of these sources, divided into five main sections. The first section provides a detailed study of contracts, exploring their essential elements: consent, subject matter, cause, and the consequences of violating contract formation rules. It is followed by an analysis of the effects of contracts and their dissolution. The second section examines unilateral will and its legislative application in Qatari civil law, while the third section focuses on tortious acts (tort liability), addressing personal liability, liability for others, and liability for damage caused by things, along with the effects of such liability. The fourth section covers unjust enrichment at the expense of others, explaining undue payment and the management of another’s affairs without their consent (negotiorum gestio). The fifth section explores the law as an independent source of obligation. Furthermore, the study compares the provisions of the Qatari Civil Code with other Arab and foreign legal systems, particularly the French Civil Code after its recent amendments. It also reviews judicial rulings related to these legal provisions, emphasizing judgments of the Qatari Court of Cassation and providing commentary in addition to a review of several Arab rulings.