1.1. In English Dictionaries and Encyclopedias

• angel | Merriam-Webster’s Collegiate Dictionary (Eleventh Edition)
• angel | Concise Oxford English Dictionary

1.2. In Bible Dictionaries and Encyclopedias

• Angel | Easton’s Bible Dictionary
• Angel | Harper’s Bible Dictionary
• Angel | Baker Encyclopedia of the Bible
• Introduction | Dictionary of Deities and Demons in the Bible DDD
• List of Angels in the Book of Revelation Revelation 1:13–18 | Halley’s Bible Handbook
• ANGEL | International Standard Bible Encyclopedia (1915)
• Angels | The Anchor Yale Bible Dictionary
• Angel | The Lexham Bible Dictionary
• Angel | The New Bible Dictionary, Third Edition
• Angels of the Nations | Dictionary of New Testament Background
• Angels | Dictionary of Paul and His Letters
• Angels, Heavenly Beings, Angel Christology | Dictionary of the Later New Testament & Its Developments

1.3. In Theological Dictionaries and Encyclopedias

• Angel | Dictionary of Biblical Imagery
• Angel | Evangelical Dictionary of Biblical Theology
• angel | The Oxford Dictionary of the Christian Church

1.4. In Theological Journals

2.1. In Systematic Theologies

• TREATISE ON THE ANGELS | Summa Theologica
• Chapter 11: The Puritans on Angels | Joel R. Beeke & Mark Jones, A Puritan Theology: Doctrine for Life
• Institutes I, xiv, 3–12 | John Calvin, Institutes of the Christian Religion
• Chapter 19: Angels | Wayne A. Grudem, Systematic Theology: An Introduction to Bible Doctrine
• Chapter XIII. Angels | Charles Hodge, Systematic Theology, Vol. 1
• Chapter 10: Good Angels | Martin Lloyd-Jones, Great Doctrines of the Bible, Vol. 1
• Appendix II: The Angels | John Miley, Systematic Theology, Vol. 2
• Angels and Spirits | William Burt Pope, A Compendium of Christian Theology, Vol. 1

2.2. In Other Books

• Contents | Every Angel in the Bible
• Contents | Angels: Elect and Evil