Revised Common Lectionary

The Revised Common Lectionary, released in 1994, runs in three-year cycles; the gospel readings in the first year (Year A) are taken from the Gospel of Matthew, those in the second year (or Year B) from the Gospel of Mark, and in the third year (or Year C) come from the Gospel of Luke. Portions of the Gospel of John are read throughout Eastertide, and are also used for other liturgical seasons including Advent, Christmastide, and Lent where appropriate.

Year A begins on the first Sunday of Advent in 2010, 2013, 2016, 2019, etc.
Year B begins on the first Sunday of Advent in 2011, 2014, 2017, 2020, etc.
Year C begins on the first Sunday of Advent in 2009, 2012, 2015, 2018, etc.