Sequential logic circuits consist of circuits requiring timing and memory devices. The basic building block for sequential logic circuits is the flip-flop. Flip-flops can be wired together to form counters, shift registers, and memory devices.

The flip-flop belongs to a category of digital circuits called multivibrators. A multivibrator is a regenerative circuit with two active devices. It is designed so that one device conducts while the other device is cut off. Multivibrators can store binary numbers, count pulses, synchronize arithmetic operations, and perform other essential functions in digital systems.
There are three types of multivibrators: bistable, monostable, and astable. The bistable multivibrator is called a flip-flop.