Proportional-Integral-Derivative (PID) is a cornerstone algorithm in control theory. The PID algorithm smoothly and precisely controls a system, such as temperature in an oven or the position of a control surface on an airplane. A PID controller works by calculating an amount of error based upon the difference between a set value and a feedback value, and provides an adjustment to the output to correct that error. The control and decision of the adjustment is done in math instead of pure logic control such as if…else statements. PID controllers have many types of uses, including controlling robotics, temperature, speed, and positioning. The basics, coding setup, and tuning of PID controllers for the Arduino platform are discussed in this chapter.