DLV is an Answer Set Programming system, based on disjunctive logic programming, which offers front-ends to several advanced KR formalisms. The system supports a language based on a logical formalisms with a very high expressive power so that programs are able to represent relevant practical problems in presence of incomplete or contradictory knowledge. The first release of the system became available in 1997, after several years of theoretical research. It has been significantly improved over and over in the last years, incorporating new features and relevant optimisation techniques in all modules of the engine. Nowadays it combines the grounder I-DLV and the solver WASP.