Principles of Physical Chemistry presents a novel approach to physical chemistry that emphasizes the use of a few fundamental principles to quantitatively describe the nature of molecules and their assemblies. It begins with atoms and molecules, using the electron-in-a-box model to illustrate the essential features of quantum mechanics and why atoms and molecules exist. Thermodynamics is not introduced in the classical manner, considering the first and second law as postulates, but approached by studying assemblies of molecules statistically. The authors proceed to molecular assemblies of increasing complexity, evolving from ideal gases to real gases and solutions, then to macromolecules and supramolecular machines, and ending with the search for the logical conditions and chemical requirements for physicochemical processes leading to life's origin, the emergence of matter that carries information. This text is ideal for both undergraduate and graduate courses in physical chemistry, providing a basis for understanding the nature of chemical processes in biology, chemistry, and engineering.