Simply stated, transcription is the process of making an RNA sequence from a segment of DNA, which is then used as a template by cellular machinery. It is the process by which a sequence of instructions is retrieved from a DNA strand, and copied into an RNA strand.

Specialized molecular machines are employed to retrieve, and copy the instruction-sequences out of the DNA strand into mRNA strands. The mRNA conveyed instruction-sequences are then used by other molecular machinery, which follow them to produce the three-dimensional protein structures that make up all biological substances. This includes the molecular machines discussed here, as well as many other molecular machines used in cell functions.

New information can also be written into a DNA molecule from an RNA molecule in a process called reverse transcription.