Introductory

• Purgatory | The Encyclopedia of Christianity, Volume 4
• Souls in Purgatory | The Dream of Gerontius
• Purgatory | The Moody Handbook of Theology
• Afterlife | The New Dictionary of Catholic Spirituality
• Purgatory | The New Dictionary of Theology
• Purgatory by Kaufmann Kohler | Jewish Encyclopedia
• The Great Divorce by C.S. Lewis

Jewish resources

• Babylonian Talmud Shabbat 2:6, II.17.N | The Babylonian Talmud: A Translation and Commentary
• Babylonian Talmud Rosh Hashshanah 16B | The Babylonian Talmud: A Translation and Commentary

Early Church Fathers resources

• The Pseudo-Clementine Homilies 3, 6 | Ante-Nicene Fathers, Volume VIII
• City of God 21.13 | Nicene and Post-Nicene Fathers First Series, Volume II
• The Enchiridion 69 | Nicene and Post-Nicene Fathers First Series, Volume III

Medieval resources

Theology

• Purgatory | Fundamentals of Catholic Dogma
• Heaven, Purgatory, and Hell | Death and Afterlife: A Theological Introduction
• Of the Modes of Supplementing Satisfaction – viz. Indulgences and Purgatory | Institutes of the Christian Religion
• The Final Purification, or Purgatory | Catechism of the Catholic Church
• Decree Touching Purgatory | The Canons and Decrees of the Council of Trent
• How many are the Places in which Souls, placed out of the Reach of Bliss, are detained after Death | The Catechism of the Council of Trent
• The Purgatory | Coptic Orthodox Diocese of the Southern United States

Art

• The Divine Comedy: The Inferno, The Purgatorio and The Paradiso by Dante Alighierei
• Hamlet in Purgatory by Stephen Greenblatt