Originally a collection of four published volumes meant to introduce the history, theology, and practice of the Orthodox Church to both inquirers and high school students, this series by Fr. Thomas Hopko is now available online for free.
This is probably one of the most comprehensive and easiest-to-read introductions to all major aspects of the Church available in English.
The areas covered in each volume are:
- Preface. Written by His Beatitude, Metropolitan Tikhon
- Volume I – Doctrine. Volume 1 contains three sections: the sources of Christian Doctrine, the main doctrines of the Orthodox Church present by way of commentary on the Nicene Creed, and an explanation of the doctrine of the Holy Trinity.
- Volume II – Worship. Volume 2 contains five sections: the Church building, the Sacraments, the Daily Cycles of Prayer, the Church Year, and the Divine Liturgy.
- Volume III – Bible and Church History. Volume 3 contains one section on the contents and interpretation of the Bible, and one section on the history of the Church, emphasizing the main theological, liturgical and spiritual development of each century.
- Volume IV – Spirituality. Volume 4 deals with the main themes of Christian Life: prayer, fasting, repentance, the virtues, witness in the world, and communion with God.