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Polytheism is belief in, or worship of, multiple gods or divinities. The word comes from the Greek words poly+theoi, literally "many gods." Most ancient religions were polytheistic, holding to pantheons of traditional deities, often accumulated over centuries of cultural interchange and experience. The belief in many gods does not preclude the belief in an all- powerful all-knowing supreme being. Present-day polytheistic religions include Hellenismos, Shinto, some forms of Wicca, and Asatru.
Jenny Blain's 2004 article, An Understanding of Polytheism, is an excellent resource on the subject.