Software engineers and interaction architects need to cooperate with each other in order to create software products that work, and that are usable and useful for the target audience. A look at reality shows that the cooperation does not function as smoothly as it should. The cause for this can be on the engineer’s side, or on the designer’s — or on both sides. This paper identifies some differences in the mentalities that make it difficult to work together in one product team.It needs to be said that successful product teams have many more components than just engineering and user interface design. To use Don Norman’s metaphor: it is technology, marketing, and user experience that make up the three legs of a solid product. We also have to add product management, quality management, documentation, customer support, and upper management to the picture. Nevertheless, this paper focuses only on the relation between developers and HCI professionals. [continue]