This introduction to quantum field theory (QFT) is written by a physical chemist for physical chemists, chemical physicists, and other non-physicists with knowledge of quantum theory but who want to explore ways in which they might use the power of QFT in their investigations. This book starts where many graduate courses in quantum theory that are offered to chemistry students leave off and first develops some of the necessary tools, such as Fock algebra, which is applied to solving the quantum oscillator problem. Then it is used to develop the theory of coherent states, time-dependent perturbation theory, and the treatment of bosons and fermions. With this background, the QFT of a perfect gas is derived and a connection to thermodynamics is demonstrated. Application to imperfect gases provides a new approach to modelling gas-liquid phase transitions. The book concludes with photons and their interaction with molecular ensembles, and brings us to full circle by deriving the blackbody radiation law, which started it all. The power of the QFT methodology and the breadth of its applications should fascinate the reader as it has the author.