The litya, or lity (“supplication”) consists of hymns and prayers, and is prescribed for all of the great feasts and most major feasts as well as all Sundays. In practice the litya is often omitted on Saturday evenings unless a feast calling for a litya also falls on the same day. The typikon (“book of models” which provides the plan for the Church’s services) often leaves it to the discretion of the rector or superior whether a litya will be served on a given day.
On ordinary Saturday evenings (without the simultaneous occurrence of any other feast), one hymn of the temple is sung, then glory and now, and the theotokion. If the temple is in the name of Christ or the Theotokos, the order will be different.
At great feasts, the hymns of the litya are all festal. On other major feasts, the first litya hymn is of the temple, and the rest are of the feast.
The blessing of bread, wheat, wine, and oil associated with the litya takes place later in vespers.
The singing of “Lord, have mercy” is often limited to 12 times after each petition, but in the service books the specified number of “Lord have mercies” varies between 30, 40, and even 50 for the different petitions.
For more about the specific hymns sung at the litya on various days, see the Tables that supply this information.