This book offers a simplified physical treatment of the kinetic theory of gases and magnetoplasmas. The text uses mean-free-path arguments when applicable and identifies problem areas where existing theory has either failed or has fallen short of expectations. Examples are provided by strong shock waves, ultrasonic waves (high Knudsen numbers), and transport across strong magnetic fields. The text pays particular attention to pressure, explaining the importance of allowing for its collisional nature from the outset in developing kinetic theory. In traditional theory, pressure is defined as a momentum flux, bypassing its collisional nature, and while this omission usually has no adverse practical effects, it leads to errors with increasing Knudsen numbers. The text is an indispensable introduction to the field for students in kinetic theory, physics, and applied mathematics, as well as to plasma researchers interested in transport phenomena.