PDDL4J is an open source library under LGPL license. The purpose of PDDL4J is to facilitate the development of JAVA tools for Automated Planning based on PDDL language (Planning Domain Description Language). Automated planning and scheduling, in the relevant literature often denoted as simply planning, is a branch of artificial intelligence that concerns the realization of strategies or action sequences, typically for execution by intelligent agents, autonomous robots and unmanned vehicles. PDDL was originally developed by Drew McDermott and the 1998 planning competition committee. It was inspired by the need to encourage the empirical comparison of planning systems and the exchange of planning benchmarks within the community. Its development improved the communication of research results and triggered an explosion in performance, expressivity and robustness of planning systems. PDDL has become a de facto standard language for describing planning domains, not only for the competition but more widely, as it offers an opportunity to carry out empirical evaluation of planning systems on a growing collection of generally adopted standard benchmark domains. The emergence of a language standard will have an impact on the entire field, influencing what is seen as central and what peripheral in the development of planning systems. The library contains: A PDDL 3.1 parser and HDDL 1.0 parser and all the classes need to manipulate its concepts. The parser can be configured to accept only specified requirements of PDDL od HDDL language. A set of useful pre-processing mechanisms in order to instantiate and simply actions into ground actions based on inertia properties. A set of already implemented classical heuristics. Several examples of planners using PDDL4J such as FastForward.