Clustered regularly interspaced short palindromic repeats (CRISPR) systems have revolutionized the life sciences since their development as an experimental tool in 2012. Native CRISPR systems act in prokaryotes as an adaptive immune system against invading genetic elements, such as viral DNA. These systems recognize invading nucleic acids, insert segments of the sequence in the host genome, and use these sequences to recognize and destroy the viral element if the cell is invaded again. In recent years, proteins from CRISPR systems, particularly the Cas9 nuclease, have been repurposed for different applications, such as gene editing experiments, large scale genetic screens, and imaging of DNA elements. CRISPR systems have dramatically increased the ease and efficiency of genome engineering, and further investigation and development of these systems is likely to continue for years to come.