Systems that act autonomously in the environment have to be able to integrate three basic behaviors: planning, execution, and learning. Planning involves describing a set of actions that will allow the autonomous system to achieve high utility (a similar concept to goals in high-level classical planning) in an unknown world. Execution deals with the interaction with the environment by application of planned actions and observation of resulting perceptions. Learning is needed to predict the responses of the environment to the system actions, thus guiding the system to achieve its goals. In this context, most of the learning systems applied to problem solving have been used to learn control knowledge for guiding the search for a plan, but very few systems have focused on the acquisition of planning operator descriptions. In this paper, we present an integrated system that learns operator definitions, plans using those operators, and executes the plans for modifying the acquired operators...