“…A turning point in the approach to the analysis of the optimal design of R&D activities along several dimensions at the same time can be perhaps identified in the attention recently devoted to the role of complementarities (Vives, 1990;Milgrom and Roberts, 1990;Amir, 1996). This toolkit has been used to investigate the presence of complementarities within R&D portfolios in monopoly (Athey and Schmutzler, 1995;Lambertini and Orsini, 2000;Lambertini, 2003Lambertini, , 2004Lin, 2004;Mantovani, 2005) or oligopoly (Bonanno and Haworth, 1998;Lin and Saggi, 2002;Rosenkranz, 2003). The bottom line of this stream of research is that R&D efforts in each direction boosts the firms' incentive to carry out analogous effort in the other direction.…”