The laws of statistical mechanics and thermodynamics form one of the most fascinating branches of physics. This new edition discards the historical approach of treating thermodynamics and statistical mechanics as separate disciplines in favor of an integrated approach. This leads more directly to a deeper understanding of the statistical nature of the thermodynamic laws, it emphasizes the atomic nature of matter, and it is a faster method of learning the subject. This revised edition has two major changes: More attention is given to the Gibbs distribution, leading to a fuller discussion of chemical reactions; and magnetic systems are introduced.