Trinity Sunday is the first Sunday after Pentecost in the Western Christian liturgical calendar, and the Sunday of Pentecost in Eastern Christianity. Trinity Sunday celebrates the Christian dogma of the Trinity, the three Persons of God: the Father, the Son, and the Holy Spirit.^[1]

Trinity Sunday is celebrated in all the Western liturgical churches: Roman Catholic, Anglican, Lutheran, (most) Presbyterians, Methodists, and many churches within the Cooperative Baptist Fellowship.

All Saints' Day (in the Roman Catholic Church officially the Solemnity of All Saints and also called All Hallows or Hallowmas^[3]), 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 honour of all the saints, known and unknown. In the Western calendar it is the day after Halloween and the day before All Souls' Day.

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 Catholic Church and many Anglican churches, the next day specifically commemorates the departed faithful who have not yet been purified and reached heaven. Christians who celebrate All Saints' Day and All Souls' Day do so in the fundamental belief that there is a prayerful spiritual bond between those in purgatory (the 'Church Suffering'), those in heaven (the 'church triumphant'), and the living (the 'church militant'). Other Christian traditions define, remember and respond to the saints in different ways; for example, in the Methodist Church, the word "saints" refers to all Christians and therefore, on All Saint's Day, the Church Universal, as well as the deceased members of a local congregation, are honoured and remembered.^[2][4]