This is an advanced study of systems of propositional logic which offers a comprehensive account of a wide variety of logical systems and which encourages students to take a critical stance towards the subject. A great variety of systems and subsystems are defined and compared as regards their deductive power and relation to their model theory. Interesting features include a more refined treatment of modal logic and the special attention given to the weakenings of classical logic. Useful appendices provide a topical bibliography and review of basic set theory.