Gene editing seeks to change DNA sequences within living cells. Gene editing has the potential to correct inherited or acquired genetic errors. To change a DNA sequence, two basic steps are required: first, to locate the DNA sequence of interest, and second, to correct that DNA sequence. We search for specific DNA sequences using proteins that naturally recognize DNA sequences. Several of these proteins can be reprogrammed to recognize a desired DNA sequence, thereby enabling the location of genes with mutations. Mutated DNA sequences can be corrected in many ways, including introducing a controlled DNA break, the most common form of gene editing. This controlled break, referred to as a DNA double-strand break, enables, in general, four types of changes.