A multiplexer, also known as a data selector, is an electronic device that selects between several analog or digital input signals and forwards the selected input to a single output line. It is a multiple-input, single-output switch that allows multiple analog and digital input signals to be routed. Multiplexers are used to implement Boolean functions of multiple variables and are part of computer systems to select data from a specific source, such as a memory chip or a hardware peripheral. They can also be used in digital communications to allow several connections over a single channel, by connecting the multiplexers single output to the demultiplexers single input (Time-Division Multiplexing).

Multiplexers can be used to share one device or resource, for example, one analog-to-digital converter or one communications transmission medium, instead of having one device per input signal. In analog circuit design, a multiplexer is a special type of analog switch that connects one signal selected from several inputs to a single output.

Multiplexers can assist with decreasing the expense of advanced circuits by reducing the number of parts required, save time in digital circuits by decreasing the number of parts that should be wired together, and are highly flexible and can be utilized in a great many applications. However, they have some disadvantages, such as a limited number of data sources that can be handled by a multiplexer, delay in the signal path, and complexity.

Multiplexing is also a method used by networks to consolidate multiple signals or streams of information over a communications link at the same time in the form of a single, complex signal. When the composite signal reaches its destination, it is demultiplexed, and the individual signals are restored and made available for processing. Multiplexing is used in a wide range of industries to facilitate both analog and digital communications, such as radio, television, telephone, and computer networks.