This book covers the essential theories of thermodynamics supported by a large number of solved examples to enhance the vision of the students towards application of thermodynamics in engineering practice. Knowledge of thermodynamics is an essential for students in branches such as mechanical and aerospace engineering, as it relates to the tog level design aspects of many devices that they will encounter. The first level course in a sequence of courses on thermodynamics is quite important since almost all the concepts are taught in this course. Higher level courses deal with applications and their realizations in practical devices. There are three principal laws of thermodynamics which are described on separate slides. Each law leads to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system. We will present some simple examples of these laws and properties for a variety of physical systems, although we are most interested in thermodynamics in the study of propulsion systems and high speed flows. Fortunately, many of the classical examples of thermodynamics involve gas dynamics. Unfortunately, the numbering system for the three laws of thermodynamics is a bit confusing. We begin with the zeroth law. The book is written in simple and lucid language and shall meet the requirements of undergraduate students of engineering and technology studying in various institutes/universities across the globe