CRISPR–Cas (clustered, regularly interspaced short palindromic repeats–CRISPR-associated proteins) is an adaptive immune system in many archaea and bacteria that cleaves foreign DNA on the basis of sequence complementarity. Here, using the geminivirus, beet severe curly top virus (BSCTV), transient assays performed in Nicotiana benthamiana demonstrate that the sgRNA–Cas9 constructs inhibit virus accumulation and introduce mutations at the target sequences. Further, transgenic Arabidopsis and N. benthamiana plants overexpressing sgRNA–Cas9 are highly resistant to virus infection.