Since 2006 the authors of this book have been sharing the teaching of an advanced course on nonequilibrium statistical physics at the University of Florence, Italy. This is an advanced course for students in the last year of the master's thesis curriculum in physics, which is attended also by PhD students. If the reader of this Preface is a colleague or a student who already attended a similar course, he or she should not be astonished by the following statement: this book was primarily conceived to organize the contents of our course, because the offer of textbooks on nonequilibrium statistical physics is typically much more limited and specialized than in the case of equilibrium statistical physics. From the very beginning it was clear in our minds that we had to aim at a textbook written for students, neither for experts nor for colleagues. In fact, we believe that a textbook on advanced topics written for the benefit of students can also be useful for colleagues who want to approach these topics, while the contrary does not hold. We dare, indeed, to say that if a book is written devoting special consideration for the understanding of students, it could be beneficial for the whole scientific community. After these preliminary remarks, which should be taken as an omen more than a statement, we want to illustrate and justify the contents of this textbook.

When we started to think about that, the first question that came to our mind was the following: what should it contain? As one could expect, the answer was not unique. It depends not only on our personal taste and interest, but it is also inspired by a sort of “tradition,” which changes significantly from university to university as well as from country to country. This is why, after having produced a preliminary list of topics, we asked for the opinion of some Italian and foreign colleagues. Honestly, we did not change that much of the preliminary list after having received their advice, partly because they did not raise strong criticisms and also because we eventually obtained quite incoherent suggestions.