In this thesis, an attempt will be made to understand the position of Islam towards Jewish and Christian laws as they were used in the inner- and intra-Islamic debate during the Abbasid era with respect to dietary laws. In the inner-Islamic debate, Islamic scholars within a particular tradition (Sunni or Shia) debate their laws internally to formulate their laws. This they do, paying close attention to the sources of law. It will be realized that the various schools in a particular tradition shared some resemblances in the laws they formulated, and this often was because they were very close to the sources they adhered to. Whenever there were differences, they were very minor. The intra-Islamic debate is about how the Sunni and the Shia traditions began to debate among themselves on the dietary laws. In their debates, the thesis explores if there were instances they used Jewish and Christian laws. By their use of these laws, this study seeks to find out how Sunnis and Shias differed and disagreed as they related to Jews and Christians in their dietary laws. The thesis focuses on two aspects of the dietary law: the laws regulating animal selection categorized into prohibited and permitted animals, and the laws regulating animal slaughtering in Islam. The laws regulating animal selection categorized into prohibited and permitted are to help us explore how the various schools of law selected the animals and considered them either as permitted or prohibited. It should be noted that only permitted animals qualified for a ritual slaughter. It further looks at how Sunnis and Shias differed in the kind of animals that were permitted and prohibited. As a consequence, the study delves into how Jewish and Christian laws affected Sunnis and Shias and to understand the reasons for their closeness and their differences. The other aspect is the laws regulating animal slaughtering in Islam. This aspect will explore the various attitudes of the schools of law regarding the person who is qualified to slaughter, the name to be mentioned when slaughtering and the manner of the slaughter. The debate initially is to settle within each school (Sunni or Shia) the importance of the invocation of the name of God and how they relate towards the meat slaughtered by Jews and Christians. That will be the inner-Islamic debate. The intra-Islamic debate will look into how Sunnis and Shias regard the meat slaughtered by Jews and Christians. This intra-debate will reveal that Sunnis are very tolerant and open towards the meat slaughtered by Jews and Christians. This they support using the Quranic text in Surah 5:5. The Shias, unlike the Sunnis, are not tolerant and are closed towards the meat slaughtered by Jews and Christians. It will also reveal that according to Sunnis there is a difference between non-Muslims, Jews, and Christians whereas Shias consider all of them as non-Muslims. It will further inform us that Shias consider Sunnis not to be proper Muslims because they eat of the meat slaughtered by Jews and Christians.