Commercial controllers with a proportional–integral–derivative (PID) control algorithm were introduced back in the 1940s. As it has been widely reported elsewhere, 80 years later PID is still the most common control algorithm used in the processes industry. In this article, fundamentals of PID control are outlined. Starting from the elemental constituent control actions that are at the core of the basic control law, additional considerations, functionalities, and implementation facts are also introduced. Afterward, special attention is placed on the considerations regarding PID‐based feedback control loops. Although the central concept of PID control can be gleaned from an examination of how these three terms are blended to form a control signal, the intelligent application of PID control in any given case requires an understanding of the process dynamics at hand as well of the achievable feedback properties.