The Babylonian summa immeru ('If the Sheep') omens are concerned with ominous signs drawn from the behaviour of the sacrificial sheep at the time of its sacrifice. They are part of the diviner's craft of divination and are related to the technique of extispicy (i.e., the examination of the entrails). The literary history and the transmission of the summa immeru omens is long and convoluted. The omens are attested from the Old Babylonian period to almost the very end of cuneiform civilization at Seleucid Uruk. Manuscripts of the omens and of their commentaries arrive from Babylonia, Assyria, Anatolia and Northern Syria. This book is the first comprehensive study of this omen genre. It offers complete text editions and commentaries of the omens, some previously unpublished. It places the summa immeru omens within the context of Babylonian divination, and investigates how texts reached a "canonical" status that had become immune from changes during millennia of textual production, transmission and reception.