Control system is an essential element of the daily process in modern culture. Control system manages the different appliances (entertainment and environments) and controls the industrial progressions and transportation schemes. Therefore, it controls our land air, sea and space explorations. Digital controllers are used in most applications with microprocessors, computers, and digital electronics. So, each electrical, mechanical or chemical engineer ought to be familiar with the digital controller's basic theory. This paper will study different research techniques about well known controllers; Proportional-Integral-Derivative (PID) controllers. So, it will summarize their structure and their recent developments. After that, new tuning algorithm will be explored using several techniques or change PID controller structure to match several systems' requirements.