In this article, the Activity Theory (AT) is analyzed to take it as a basis for the definition of an Activity classification Model of Interactive Systems called: Activity Taxonomy (ATx) for Interactive Systems. Our purpose is to use the ATx for: a. The incorporation of the Human Computer Interaction (HCI) in the processes of software development, b. Definition of the minimum activity classifiers to specify interactive systems that promote HCI, c. Evaluation and integration of languages and/or software development processes, d. The specification of the execution models of interactive systems.