This book constitutes the refereed proceedings of the 4th International Workshop on the Theory and Applications of Formal Argumentation, TAFA 2017, held in Melbourne, VIC, Australia, in August 2017. The workshop was co-located with International Joint Conference on Artifi cial Intelligence (IJCAI 2017). The 15 revised full papers presented were carefully reviewed and selected from 20 submissions. The workshops covers the subjects such as non-monotonic reasoning, decision making, inter-agent communication, the semantic web, grid applications, ontologies, recommender systems, machine learning, neural networks, trust computing, normative systems, social choice theory, judgement aggregation and game theory, and law and medicine.