Theresian Missionaries of Mary

All Saints' Day (in the Roman Catholic Church officially
the Solemnity of All Saints
and also called All Hallows or Hallowmas^[1]),
often shortened to All Saints, is a solemnity celebrated
on 1 November by parts of Western Christianity,
and on the first Sunday after Pentecost in Eastern Christianity,
in honor of all the saints, known and unknown.

In Western Christian theology, the day commemorates
all those who have attained the beatific vision in Heaven.
It is a national holiday in many historically Catholic countries.
In the Roman Catholic Church, the next day,
All Souls' Day,
specifically commemorates the departed faithful
who have not yet been purified and reached heaven.
Catholics celebrate
All Saints' Day and All Souls' Day
in the fundamental belief
that there is a prayerful spiritual communion
between those in the state of grace
who have died and are either being purified in purgatory
or are in heaven (the 'church penitent' and the 'church triumphant',
respectively), and the 'church militant' who are the living.
Other Christian traditions define,
remember and respond to the saints in different ways.

Eastern Christians of the Byzantine Tradition follow the earlier tradition of commemorating all saints collectively on the first Sunday after Pentecost,
All Saints' Sunday.

The feast of All Saints achieved great prominence in the ninth century,
in the reign of the Byzantine Emperor, Leo VI "the Wise" (886.911).
His wife, Empress Theophano.commemorated on December 16.lived a devout life.
After her death in 893,^[2]
her husband built a church, intending to dedicate it to her.
When he was forbidden to do so,
he decided to dedicate it to "All Saints," so that if his wife were in fact one of the righteous,
she would also be honored whenever the feast was celebrated.
^[3] According to tradition,
it was Leo who expanded the feast from a commemoration of All Martyrs
to a general commemoration of All Saints,
whether martyrs or not.

This Sunday marks the close of the Paschal season.
To the normal Sunday services are added special scriptural readings
and hymns to all the saints (known and unknown) from the Pentecostarion.

The Sunday following All Saints' Sunday.
the second Sunday after Pentecost.is set aside as a commemoration of all locally venerated saints,
such as "All Saints of America", "All Saints of Mount Athos", etc.
The third Sunday after Pentecost may be observed for even more localized saints,
such as "All Saints of St. Petersburg", or for saints of a particular type,
such as "New Martyrs of the Turkish Yoke."

In addition to the Sundays mentioned above,
Saturdays throughout the year are days for general commemoration of all saints,
and special hymns to all saints are chanted from the Octoechos.

http://www.catholic.org/saints/allsaints/