Statistical and thermal physics have become even more important than when the first edition of our text was published in 2010. Many of the tools and ways of thinking that we discuss are helpful in understanding the relationship between the large scale statistics of pandemics and extreme wealth inequality to small scale individual behavior. The use of probability theory and the development of models to provide insight, even though none can be perfect, are helpful in understanding and guiding our actions as a society and as individuals.

A background in statistical and thermal physics is essential for doing research in many of the hottest subfields of physics and related areas, including astrophysics, biological physics, neuroscience, and the physics of novel materials. In addition, the ubiquitous use of computers has influenced both teaching and research in statistical and thermal physics more than any other area of physics. Statistical and thermal physics are even more important in the physics curriculum than they were in 2010.

The second edition retains the key components of the first edition, including the following:

1. A focus on the conceptual foundations of statistical and thermal physics in addition to techniques for doing calculations.
2. A standalone introduction to thermodynamics and the phenomenological way of thinking.
3. A standalone introduction to probability theory necessary for understanding statistical mechanics and for understanding many problems in our everyday lives.
4. Discussion and use of computer simulations and numerical analysis throughout the text. No programming knowledge is assumed, but the algorithms used in the programs are discussed in the text.
5. More discussion of magnetic systems compared to most undergraduate texts, giving students more opportunities to apply the tools of statistical mechanics.
6. Frequent discussions of the connection between the ideas in the text and contemporary research in physics and related fields.
7. Many problems with a wide range of difficulty, including many that require the use of computer programs.
8. The origin of all results are discussed and where possible a formal derivation is given. In other cases we provide examples to illustrate the results.

The first edition of our text did deliver what we had hoped. We realize that some of the topics we discuss are usually found in graduate texts. For that reason many undergraduates found the text challenging. Our hope is that our text will provide a bridge to some of the more advanced topics, and many of these topics will motivate students to continue their studies. Our main goals for the second edition are to make the text more accessible to undergraduates and more useful for instructors. In particular, we have done the following.

1. Moved some advanced topics to the supplementary notes at the end of the chapter.
2. Reorganized the presentation in some chapters.
3. Eliminated some derivations that are not essential.
4. Encouraged active reading by replacing examples with guided problems to be worked on while reading the text.
5. Edited every chapter to eliminate typos and other errors and to improve readability.
6. Improved some of the programs and made available programs in Python and JavaScript as well as Java.
7. Added a chapter on properties such as diffusion, thermal conductivity, and viscosity for which time is relevant.

The added chapter on time dependent phenomena at the end of our text provides an introduction to kinetic theory. Many texts discuss kinetic theory in their introductory chapter so that they can derive the ideal gas equation of state and discuss various transport coefficients. We believe that it is important to emphasize the time independent properties of systems in equilibrium and that much of equilibrium statistical mechanics involves counting microstates. A discussion of time-dependent phenomena at the end of our text allows us to emphasize again the importance of fluctuations in equilibrium and their relation to the relaxation of systems near equilibrium.

We have received comments, suggestions, and corrections from students and instructors from around the world. We thank them for contacting us. Their communications have helped inform this second edition. In particular, we would like to thank Lisa Dundon, Bill Klein, Harvey Leff, Sakib Matin, Sid Redner, and students in the Thermal Physics course at Kalamazoo College. We would like to give a special thanks to Wolfgang Christian and Robert Hanson for converting the STP programs from Java to JavaScript and to Lyle Barbato and Bruce Mason for hosting the Statistical and Thermal Physics website on the AAPT-ComPADRE website.

We are grateful to Princeton University Press, particularly our editor, Ingrid Gnerlich, for their continued interest in our project.

We owe a special thanks to our friends and family, especially Patti Gould and Hillary Rettig.

We remember Louis Colonna-Romano, who after working for many years at Digital Equipment Corporation, became a graduate student at Clark University as well as a teacher at Brandeis University, Worcester Polytechnic Institute, and Clark University. Lou generated all the figures for the first edition of our text by writing them in postscript. Lou enjoyed learning, reading, and conveying his enjoyment to his students. He had carefully considered opinions on everything and could have an educated discussion on any topic, including European history, his favorite composers, Dante's Inferno, and climate change. He is missed by his students and colleagues alike.

Harvey Gould, hgould@clarku.edu

Jan Tobochnik, jant@kzoo.edu