This comprehensive text is based on the author's course notes, refined and updated over 15 years of teaching. The core of the text is two chapters on water and its transformations. Four chapters lay the foundations, from energy conservation to the ideal gas law, specific heat capacities, adiabatic processes, and entropy. The first core chapter treats phase transitions of water. A lengthy discussion of the van der Waals equation sets the stage for phase diagrams. Free energy is applied to determining the effects of dissolved substances, total pressure, and size on vapour pressure. The chapter on moist air and clouds discusses wet-bulb and virtual temperatures, isentropic ascent of saturated air, thermodynamic diagrams, stability, and cloud formation. The final chapter is on energy, momentum, and mass transfer. The book contains over 200 exercises, mostly applications of basic principles to concrete problems. History is woven into the text and molecular interpretations are given wherever possible. Assumptions are clearly exposed, derivations are detailed, and equations are interpreted physically and applied. No previous knowledge of thermodynamics or kinetic theory is assumed, although readers are expected to be well-grounded in calculus, differential equations, vector analysis, and classical mechanics.