Judaism and Christianity are two great faiths which were born, and developed, in the same geographical region, albeit at different points in history. Both of these monotheistic religions, from their beginnings in the Middle East, spread in time all over the world, Christianity following on from Judaism; today, their followers number in excess of 2 billion people. In the Jewish and Christian Holy Books - the Old Testament (including the Book of Psalms), and New Testament - it can be seen that different species of animals play a rich variety of roles. This study, by examining all of the text of the three Holy Books of these two religions, aims to reveal the roots in religion of such subjects as the importance of animals, animal rights, and animal welfare throughout the history of Judaism and Christianity.