A multiple cloning site (MCS), also called a polylinker, is a short segment of DNA which contains many (up to ~20) restriction sites - a standard feature of engineered plasmids. Restriction sites within an MCS are typically unique, occurring only once within a given plasmid. MCSs are commonly used during procedures involving molecular cloning or subcloning. Extremely useful in biotechnology, bioengineering, and molecular genetics, MCSs let a molecular biologist insert a piece of DNA or several pieces of DNA into the region of the MCS. This can be used to create transgenic organisms, also known as genetically modified organisms (GMOs).