Decoders are a simple combinatorial block that converts one form of digital representation into another. Usually, a decoder takes a smaller representation and converts it into a larger one (the opposite of encoding). Typical examples are the decoding of an n-bit word into 2n individual logic signals. For example a 3-8 decoder takes three logic signals in and decodes the value of one of the eight output signals 23 to the selected value. Multiplexers carry out the opposite function and select one bit from an n-bit word, using a selection address. This chapter will introduce and describe both decoders and multiplexers.