I remember that the idea of this book emerged ?rst in Toulouse, during the Third Conference on Energy Markets - 3 years ago now. Anna Cret` ? gave a talk on a model dealing with seasonal gas storage in the USA, and Christian Von Hirschausen was her discussant. Both of them were devoting their efforts to understand the natural gas market in Europe and the relevant liberalization process. I found their interest in storage rather original, so I encouraged Anna to collect the most original cont- butions on this topic. Back in Milan with this idea in mind, she organized a working group at IEFE- Bocconi University, where she works. Then, during the following year, she - changed ideas and organized several meetings with the book's contributors. She regularly invited the most important Italian gas sector representatives to these me- ings, to make sure that the economic models were well suited to tackle the issues at stake in the European gas industry.