The paradigm presented in this monograph is proposed as an agent programming language. It charts the evolution of the language from Prolog to intelligent agents. The monograph is divided into two parts. The first part Chapters 1-5 describe the evolution of the paradigm of GDC (Guarded Definite Clauses). The second part, Chapters 6-10 presents some applications of GDC in some detail. Notably, Chapter 1 takes an irrevent view of AI. Chapter 2 gives a retrospective rationale for the Japanese Fifth Generation. Chapter 9 describes how the overhead of meta-interpretation can ge assuaged by partial evaluation. Chapter 10 concludes with applications of GDC to robotics and multi-agent systems.