This book presents a new concurrent logic programminglanguage called Conclog and a methodology for programming init.Conclog was designed bytaking the ideal features of logicprogramming as reference, rather than by concentratingdirectly on operational tricks to ensure efficiency. Thisleads to quite easy declarative programming. Concern forsoundness and completeness ensures that multi-directionaland multi-solution correct procedures can be coded quitestraightforwardly. Assuming suitable hypotheses on theiruses, they can be transformed into very efficient versionsthanks to the introduction of appropriate controlinformation. Correctness-preserving properties are given forthat purpose.The designof Conclog involves three steps. First, a soundand complete parallel execution model of Horn clauseprograms is proposed which reduces subgoals of conjunctionsindependently and uses a calculus for reconcilinginconsistent bindings. Second, this is extended to handlenegation as completely as possible. Third, a minimal andreasonably complete set of extra-logical features aredefined for optimization and practical purposes.The second part of the book presents a methodology forconstructing Conclog in a rigorous way. This covers theentire programming process, from informal specifications vialogic descriptions to efficient programs. The methodologycan be adapted to other languages.