Intro

• Matthew Barrett. Simply Trinity (2021). [The second best book on the Trinity. This is not a beginner book but Barrett is where you should start nonetheless]

• Scott Swain. The Trinity: An Introduction (2020).

• Millard Erickson. Making Sense of the Trinity (2000).
  
  

Intermediate

• Fred Sanders. The Triune God (2016).

• Robert Letham. The Holy Trinity: In Scripture, History, Theology And Worship (2004). 

• Peter Toon. Our Triune God: A Biblical Portrayal of the Trinity (1996). 

• Thomas Torrance. One Being: Three Persons (1996); The Trinitarian Faith (1998).

• Auugustine. On the Trinity (416).

• Millard Erickson. God in Three Persons: A Contemporary Interpretation of the Trinity (1995).

Advanced

• Thomas Joseph White. The Trinity: On  the Nature and Mystery of the One God (2021). [The best book on the Trinity]

• Matthew Barrett, ed. On Classical Trinitarianism: Retrieving the Nicene Doctrine of the Triune God (2024). [The third best book on the Trinity]

• McIntosh. One God, Three Persons, Four Views: A Biblical, Theological, and Philosophical Dialogue on the Doctrine of the Trinity (2024).

• Veli-Matti Karkkainen. The Trinity: Global Perspectives (2007).

• Gundry & Sexton. Two Views on the Doctrine of the Trinity (2014).
  
  

Rejection of EFS/ESS (Eternal Functional Subordination)

Intermediate

• Matthew Barrett. Simply Trinity (2021). [The obliteration of EFS]
  
  

Advanced

• Kevin Giles. The Rise and Fall of the Complementarian Doctrine of the Trinity (2017).

• Millard Erickson. Who’s Tampering with the Trinity: An Assessment of the Subordination Debate (2009).

• D. Glen Butner Jr. The Son Who Learned Obedience: A Theological Case Against the Eternal Submission of the Son (2018).
  
  

Eternal Generation of the Son

Advanced

• Scott Swain. Retrieving Eternal Generation (2017).

• Kevin Giles. The Eternal Generation of the Son: Maintaining Orthodoxy in Trinitarian Theology (2012). 

Defense of the Filioque

Advanced

• Bruce McCormack & Thomas Joseph White. "Processions and Missions: A Aoint of Convergence Between Thomas Aquinas and Karl Barth." Thomas Aquinas and Karl Barth: An Unofficial Catholic-Protestant Dialogue (2013): 99-126. [This is the ultimate essay on the topic. I can't find an online pdf, though]

• Marl Pugliese. "How Important is the Filioque for Reformed Orthodoxy?" The Westminster Theological Journal 66, no. 1 (2004): 159-177. [His handling of the biblical text is weak, but he does a good job with the church fathers]

• Brian Daley. "Revisiting the 'Filioque': Roots and Branches of an Old Debate." Pro Ecclesia 10, no. 1 (2001): 31-62.

• Ty Kieser. "Is the Filioque an Obstacle to a Pneumatologically Robust Christology? A Response from Reformed Resources." Journal of Reformed Theology 12, no. 4 (2018): 394-412.

• David Guretzki. MA Thesis: The Genesis and Systematic Function of the Filioque in Karl Barth's Church Dogmatics (2006).

• Gerald Bray. The Filioque Clasue in History and Theolgy. The Tyndale Historical Theology Lecture, pp.91-144 (1982).

• Robert Letham. East is East and West is West? Another Look at the Filioque. Mid-America Journal of Theology 13 (2002) pp. 71-86. 
  
  

Refutation of the Filioque

Advanced

• Nick Needham. The Filioque Clause: East or West? Scottish Bulletin of Evangelical Theology.

• Robert M. Haddad. “The Stations of the Filioque,” St. Vladimir’s Theological Quarterly, 46 (2002): 209-268.