Gas discharges and non-equilibrium low-temperature plasmas form the basis for most plasma technologies. This book introduces engineering and science students to the basic underlying physics and chemistry concepts that form the foundation of plasma science and engineering. It is an accessible primer directed primarily at those students who are unaware what a plasma or gas discharge is, nor have fundamental backgrounds in statistical thermodynamics, gas dynamics, fluid dynamics, or solid-state physics to effectively understand many plasma and gas discharge principles. The second edition covers additional topics such as gas breakdown leading to plasma initiation and the formation of sheaths, and discusses these within the context of a basic description of the most common plasma type, a dc glow discharge. This text is suitable for upper level undergraduate students, graduate students, and young researchers in physics, chemistry, chemical engineering, electrical engineering, and mechanical engineering with interest in plasma science and engineering. Part of IOP Series in Plasma Physics.