Our three-year cycle of Sunday readings uses Matthew in Year A, Mark in Year B and Luke in Year C. The First Sunday of Advent, December 3, 2000, begins Year C. The Gospel of John is used each year during the Easter season and during Year B since the Gospel of Mark is shorter than the others.
The Gospel readings are chosen first; Sunday’s first reading is coordinated with it. The second reading is continuous from the previous Sunday, almost always on a different theme.
Weekday Masses have a single cycle of Gospel readings. All four Gospels are used at weekday Masses each year. The first reading on weekdays is either Year I (odd-numbered years) or Year II (even-numbered years). Weekday readings for Advent and Lent are the same each year.
Although the Lectionary (book of readings) is the same for Roman Catholics worldwide, small differences from country to country exist. For example, Italian Catholics celebrate Epiphany on January 6 while U.S. Catholics celebrate this feast on the first Sunday after January 1.
A reading can omit a few verses. This usually provides greater clarity but can raise problems about context.