The term "genome editing" refers to the application of techniques that allow a strand of DNA to be cut at a precisely defined location, thereby modifying the DNA by changing, removing or adding DNA sequences. The best known techniques of this kind include CRISPR/Cas9, ZFN and TALEN, which in this context are often referred to as "gene scissors".

CRISPR/Cas9 consists of two parts: The protein Cas9 is an enzyme with a so-called nuclease activity that enables it to completely cut through a DNA strand. Such enzymes are called restriction enzymes (also: restriction endonucleases, REN). CRISPR is an RNA molecule that binds to a precisely defined position on the DNA and thereby indicates the interface to the Cas9 nuclease. The particular advantage of CRISPR/Cas9 is that RNA molecules can be produced inexpensively and comparatively easily, making them easily accessible for research.

The zinc finger nuclease (ZFN) is a synthetic restriction enzyme. This consists of a zinc finger domain, which has the function of finding and binding to the corresponding DNA sequence, and a nuclease domain that cuts the DNA. 

TALEN (transcription activator-like effector nucleases) is also a synthetic restriction enzyme. Similar to zinc finger nuclease, it consists of a DNA-binding TAL-effector domain and a nuclease domain for cutting the DNA. 

In contrast to CRISPR/Cas9, both ZFN and TALEN have to be redesigned for each application to allow sequence-specific binding to DNA, which makes them much more complex to produce.