This text adopts a cognitive viewpoint on design, focusing on individually conducted activities actually implemented in professional, industrial design projects. It presents elements for a cognitive descriptive model of design that, on the one hand, furthers our understanding of design, and on the other hand, offers elements to people who wish to use such knowledge in order to advance education and practice of professional designers. The text is especially concerned with dynamic aspects of design -that is, it focuses on the activity implemented by designers, especially the cognitive processes and/or strategies they use- rather than with static aspects. Section 1 presents the classical cognitive viewpoint on design, that is, the symbolic information-processing (SIP) approach, represented by Herbert A. Simon. Section 2 focuses on the main alternative to the SIP approach for design, i.e. the "situativity" (SIT) approach, mainly represented by Donald Schön. Section 3 is the main division of this text. It presents nuances and critiques with respect to both SIP and SIT approaches, and completes and integrates these two approaches into our own cognitively oriented dynamic approach to design.