All Saints’ Day is celebrated on November 1st of each year. The origin of the festival of All Saints celebrated in the West dates to May 13, 609 or 610, when Pope Boniface IV consecrated the Pantheon at Rome to the Blessed Virgin and all the martyrs; the feast of the dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since.
The Feast of All Saints is a holy day of the Church honoring all saints, known and unknown. This is much like the American holidays Veterans Day and Presidents Day, where many people are honored on one day. While we have information about many saints, and we honor them on specific days, there are many unknown or unsung saints, who may have been forgotten, or never been specifically honored. On All Saints Day, we celebrate these saints of the Lord, and ask for their prayers and intercessions. The whole concept of All Saints Day is tied in with the concept of the Communion of Saints. This is the belief that all of God’s people, on heaven, earth, and in the state of purification (called Purgatory in the West), are connected in a communion. In other words, Catholic and Orthodox Christians believe that the saints of God are just as alive as you and I, and are constantly interceding on our behalf. Remember, our connection with the saints in heaven is one grounded in a tight-knit communion. The saints are not divine, nor omnipresent or omniscient. (ChurchYear.net)