Empirical studies on design have emphasised the role of memory of past solutions. Design involves the use of generic knowledge as well as episodic knowledge about past designs for analogous problems : in this way, it involves the reuse of past designs. We analyse this mechanism of reuse from a socio-cognitive viewpoint. According to a purely cognitive approach, reuse involves cognitive mechanisms linked to the problem solving activity itself. Our socio-cognitive approach accounts for these phenomena as well as reuse mechanisms linked to cooperation, in particular coordination, and confrontation/integration of viewpoints.