This article has focused on propositional dynamic logic and some of its significant variants.  There are by now a number of books—Goldblatt [1982], Goldblatt [1992a], Harel [1979] and Harel, Kozen and Tiuryn [2000]—and survey papers—Harel [1984], Kozen and Tiuryn [1990], Parikh [1983] —treating PDL and related formalisms.  The body of research on PDL is certainly instrumental in developing many logical theories of system dynamics. However, these theories are arguably out of the scope of the present article.  Van Eijck and Stokhof [2006] is a more recent overview of topics making use of dynamic logic, addressing various themes that are of certain interest for philosophers: e.g., dynamics of communication, or natural language semantics.  Recent books are going in much details on newer topics, such as dynamic logic of knowledge (dynamic epistemic logic) in Van Ditmarsch, Van Der Hoek and Kooi [2007], and the dynamic logic of continuous and hybrid systems (differential dynamic logic) in Platzer [2010].  PDL was conceived primarily for reasoning about programs. There are many other applications of modal logic to reasoning about programs. Algorithmic logic is closer to PDL since it allows one to talk explicitly about programs. The reader is invited to consult the work studied in Mirkowska and Salwicki [1987]. Temporal logics are now the chief logics in theoretical computer science and have a close connection with logics of programs. They allow one to express the temporal behavior of transition systems with a language that abstracts away from the labels (hence the programs). See for instance Schneider [2004] for an overview of the foundations in this research area.