This book provides a new, linguistic approach to Argumentation Theory. Its main goal is to integrate the logical, dialectical and rhetorical dimensions of argumentation in a model providing a unitary treatment of its justificatory and persuasive powers. This model takes as its basis Speech Acts Theory in order to characterize argumentation as a second-order speech act complex. The result is a systematic and comprehensive theory of the interpretation, analysis and evaluation of arguments. This theory sheds light on the many faces of argumentative communication: verbal and n-verbal, mological and dialogical, literal and n-literal, ordinary and specialized. The book takes into consideration the major current comprehensive accounts of good argumentation (Perelman's New Rhetoric, Pragma-dialectics, the ARG model, the Epistemic Approach) and shows that these accounts have fundamental weaknesses rooted in their instrumentalist conception of argumentation as an activity oriented to a goal external to itself. Furthermore, the author addresses some challenging meta-theoretical questions such as the justification problem for Argumentation Theory models and the relationship between reasoning and arguing.