The International Ergonomics Association defines ergonomics as “the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance” (http://www.iea.cc/ergonomics). This orientation of its program has led to diverse work within activity ergonomics. We will describe a brief panorama of this work, and arrive to the idea that one cannot limit oneself to designing artifacts. Design is a process of joint development of artifacts and of the activity of those who use them. The goal of this text is to propose a dialogical approach of mutual learning between workers and designers, aiming to address the challenge of a developmental approach to design.