First Steps in Modal Logic
Sally Popkorn
Cambridge University Press
This is a graduate-level text for a first course in propositional modal logic.  It is written from the semantical point of view rather than the more usual proof theoretic approach, and the book covers all basic material including the propositional languages, the semantics and correspondence results, and proof systems and completeness results--as well as some topics not usually covered in a modal logic course, such as bisimulation. Important features of the book are the many exercises and extensive set of solutions that are included.