monotheism is the belief in only one god, rather than two or more, which would be polytheism such as ancient greece, ancient rome, ancient egypt and partly hinduism. many religions are monotheistic, such as judaism, christianity, islam, baha'i faith, sikhism, eckankar, zoroastrianism, cao dai and tenrikyo. some pagan and neo-pagan religions are also monotheistic. deism is the belief that a higher being like god exists, but rejects the belief in many gods, revelation, religions, rituals, sacred books (like the bible or quran), prophets (like jesus or muhammad), etc. judaism and zoroastrianism are thought to be the oldest living monotheistic religions.