A lectionary is simply a pre-determined schedule of which readings to use on each Sunday of the year (as well as on other special days). The Revised Common Lectionary is used by most mainline Protestant churches (Presbyterian, UCC, Lutheran, Reformed, Methodist, Episcopal/Anglican, Disciples of Christ, and others).

In the Revised Common Lectionary, each Sunday is given 4 scriptural selections: 

• a reading from the Hebrew Bible (a.k.a. the Old Testament)
• a selection from the book of Psalms (that is intended as a response to the first reading)
• a reading from the New Testament letters (a.k.a. epistles)
• a reading from one of the four books of the Bible known as 'the Gospels' (Matthew, Mark, Luke, or John). 

The cycle is 3 years long, with each year of the cycle focusing more heavily on a different set of books from the Bible.

By using a lectionary, we are able to follow the pattern of the church year, taking us from the coming of the Messiah in Advent (the weeks leading up to Christmas), to Jesus' journey to Jerusalem and the cross during Lent (the weeks leading up to Easter), to the Holy Spirit empowering the church at Pentecost some 50 days after Easter. The readings for the rest of the year (called "Ordinary Time") offer a wide variety of groupings allowing for different themes to be examined and preached. 

For more information on the Revised Common Lectionary click here.