Clustered regularly interspaced short palindromic repeat/CRISPR-associated 9 (CRISPR/Cas9) enables targeted genome engineering. The simplicity of this system, its facile engineering, and amenability to multiplex genes make it the system of choice for many applications. This system has revolutionized our ability to carry out gene editing, transcription regulation, genome imaging, and epigenetic modification. In this review, we discuss the discovery of CRISPR/Cas9, its mechanism of action, its application in medicine and animal model development, and its delivery. We also highlight how the CRISPR/Cas9 system can affect the next generation of drugs by accelerating the identification and validation of high-value targets. The generation of precision disease models through this system will provide a rapid avenue for functional drug screening.