The work reported here introduces Defeasible Logic Programming(DeLP), a formalism that combines results of Logic Programming andDefeasible Argumentation. DeLP provides the possibility ofrepresenting information in the form of weak rulesin a declarative manner, and a defeasible argumentation inferencemechanism for warranting the entailed conclusions. In DeLP anargumentation formalism will be used for deciding betweencontradictory goals. Queries will be supported by arguments thatcould be defeated by other arguments. A query $q$ will succeed when there is anargument ${\mathcal A}$for $q$ that iswarranted, i.e. the argument ${\mathcalA}$ that supports $q$ is found undefeated by a warrant procedurethat implements a dialectical analysis. The defeasible argumentationbasis of DeLP allows to build applications that deal with incompleteand contradictory information in dynamic domains. Thus, theresulting approach is suitable for representing agent's knowledgeand for providing an argumentation based reasoning mechanism toagents.