The Bible emphasizes throughout that there is only one God.  "Hear, O Israel: The Lord our God, the Lord is one.  Love the Lord your God with all your heart and with all your soul and with all your strength."(1)

But even in the Old Testament there are hints of a diversity and a plurality within this One.  For example, at the creation, God says, "Let us make man in our image, in our likeness, ..."(2) Another hint comes from the appearances of the "Angel of the Lord" - identified with God, and yet distinct from God.(3)

In the New Testament, though, this is revealed more fully.  Here it becomes clear that the One is also Three: God the Father, God the Son and God the Holy Spirit.

Careful wording is needed to avoid confusion about this.  Each of the Three is fully divine and yet there are not three Gods.  One way of phrasing this is to say that God is three persons existing eternally in one single being or nature.  The word Trinity does not appear in the Bible but is a useful shorthand for this.

The New Testament also reveals that there is an order within the Three - the Son is sent by the Father, and the Holy Spirit is sent by the Father and the Son.(4) This doesn't mean that any one of the Three is less important or less divine than the others; rather it points to the humility and harmony that exists within the Trinity.

Over a period of 60 years or so, the early church debated the Bible's teaching about the Trinity in what has become known as the Arian controversy.  This debate culminated in 381AD with the formulation of the Nicene Creed - a declaration of orthodox Christian belief that has been treasured ever since.

The teaching that Jesus is both God and man is discussed separately.