The "Participatory design" approach, typically in use in the design of software, aims to integrate, as far as possible, expectations from future users, for instance in terms of available features and ergonomy. Within this framework, what matters is the interaction between the designers and the future users of a technology. In this respect, the "Participatory design" approach aims to initiate a dialogue between both. It is not only a matter of discussing broadly about the project, but rather of engaging with its technicalities and materialities. This approach takes "co-construction" seriously and takes it that designers are no more competent than future users, precisely when it comes to the question of usability. So, future users here appears as "usability experts" who know what they expect from a technology, which tasks it should perform to serve their needs and how it should be designed.