There is One God, who is Father, Son, and Holy Spirit.
The Trinity is a controversial doctrine; many Christians admit they don't understand it, while many more Christians don't understand it but think they do.
In fact, although they'd be horrified to hear it, many Christians sometimes behave as if they believe in three Gods and at other times as if they believe in one.
Trinity Sunday, which falls on the first Sunday after Pentecost, is one of the few feasts in the Christian calendar that celebrate a doctrine rather than an event.
