Abstract
A Kleene algebra is an algebraic framework to handle regular languages. Considering that regular expressions appear everywhere in fields of computer science, it may be easy to infer that a Kleene algebra can captures properties of natural class of structures appear in computer science. Since Kleene algebras are defined by equations and Horn clauses, if a phenomenon is interpreted in Kleene algebra, reasoning of the phenomenon is performed by simple transformations of expressions. We introduce basic properties and application examples of Kleene algebras to theory of programs.