Facing the challenges of energy transition, communication, mobility of goods and people, and more generally of competitiveness in a globalized world, European Member States engaged in the development of infrastructure networks supporting the common market. In this perspective, the integration of network industries in Europe, which translates into the creation of common energy, transportation and telecoms markets without internal borders, is usually analysed in terms of market design and / or regulatory design. In both perspectives, firms' strategies are often ignored or, at best, taken as responses to changing market and regulation conditions. However, we argue here that firms, through their strategies on the market, for structuring markets and in the non-market environment, participate proactively in the European integration of network industries. Therefore, the articulation of market design, regulatory design and strategic design leads us to formulate the following research question: how firms operating in European network industries do integrate market and regulatory change into their strategy? First, analysing the integration process in both air transport and electricity at the institutional level has allowed us to characterize what we called the "regulatory cycle", which underlies the production of legislative packages punctuating industries restructuring. Second, analysing strategic choice of cooperation and competition in the railway sector has led us to develop a tool for qualitative analysis of strategic alliances, "Multidimensional Strategic Sequences applied to Alliances" (MSSA). MSSA allow taking into account the interdependencies between firms in a multimarket framework. Finally, analysing an electricity interconnection project undertaken by a private operator has led us to develop the concept of "strategic situation", characterized by a particular configuration of actors, strategic spaces and strategic times. Thus, taking into account the risks associated with the regulatory cycle and market developments suggest that firms should concentrate on developing sequential short-term strategies tailored to the changing parameters of strategic situations.
