Nicene Christianity is a set of Christian doctrinal traditions which reflect the Nicene Creed, which was formulated at the First Council of Nicaea in AD 325 and amended at the First Council of Constantinople in AD 381.
At the time of the First Council of Nicaea, the main rival of Nicene Christian doctrine was that of Arianism, which became eclipsed during the 7th century AD with the conversion of the Gothic kingdoms to Nicene Christianity. The main points of dissent between the two centered on Christology, or the nature of Jesus' divinity. Nicene Christianity regards Jesus as divine and co-eternal with God the Father, while Arianism treats him as the first among created beings and inferior to God the Father. Various other non-Nicene doctrines and beliefs have existed since the early medieval period, all of which have been considered heresies.
Today's mainstream Christian churches (including all of the Catholic, Eastern Orthodox, Oriental Orthodox, Assyrian and Ancient churches, Lutheran and Anglican churches, as well as most Protestant denominations) adhere to the Nicene Creed and thus exemplify Nicene Christianity.
Chalcedonian Christianity forms a large subset of Nicene Christianity. In addition to subscribing to the Nicene Creed, Chalcedonian Christians also subscribe to the decisions of the First Council of Ephesus in AD 431 and of the Council of Chalcedon in AD 451. Most Nicene Christians also adhere to the beliefs of Chalcedonian Christians, as defined by the Chalcedonian Creed. However, those denominations that hold to the Nicene Creed, but do not adhere to the Chalcedonian Definition (or the Chalcedonian Creed), include portions of Eastern Christianity (i.e., the Oriental Orthodox Churches and, historically, the Church of the East [which also rejects the outcome of the First Council of Ephesus]) and would therefore be considered non-Chalcedonian Nicene Christians.
Today, examples of non-Nicene Christian denominations encompass both Protestant and non-Protestant non-trinitarian groups. Examples of these groups include the majority of the Latter Day Saint movement (with the exception of the Nicene Mormon group known as the Community of Christ [formerly known as the Reorganized Church of Jesus Christ of Latter Day Saints]), the Unitarian Church of Transylvania, Oneness Pentecostals, and others.