Generally logic gates have just two operating modes/states, either 0 or 1, that means purely digital (or binary). In some of the applications, we need another additional state, which is known as high-impedance (high-Z) state. The device with three operating modes is termed as tri-state logic gates. To understand the tri-state concepts, let us primary study how are digital logic gates realized with the help of simple switch then we shall proceed with the essential additional circuits to realize tri-state logic gates. We shall consider the manual operation of the switch for simple understanding of these basics. But in real digital circuits these switches are realized using transistors.