"This book is intended to serve both the neophyte and the already initiated in understanding the methods, tools (algebras and relational structures), and results of propositional modal logic. At the heart of the matter lies the unimodal modal logic K and its class of quasinormal extensions. Another family of logics which appears in a prominent secondary role is the class of superintuitionistic logics, the logics which are extensions of Heyting's intuitionistic logic Int. From several points of view superintuitionistic logics are very closely related to modal logics. The authors' goal is to present a systematic exposition of the most important methods and results concerning these two classes." --Mathematical Reviews

"The book is certainly well-structured and any student or researcher mastering its contents will be well equipped to tackle technical problems in modal logic. Each chapter has an ample supply of good exercises and finishes with adequate and interesting historical notes. I think this is a great work and I am very glad to have it. A modern textbook on the mathematics of modal logic was long due, and this work fills the gap perfectly. I expect that it will become one of the standard references in the field of modal logic." -- Yde Venema, The Philosophical Review, Vol 109, No 2, Apr 2000