Genome editing using nucleases such as CRISPR-Cas induces programmable DNA damage at a target genomic site, but can also affect off-target sites. We develop a powerful assay for the unbiased identification of off-target sites that we term DISCOVER-seq. This approach takes advantage of the recruitment of endogenous DNA repair factors for genome-wide identification of Cas-induced double strand breaks. One such factor, MRE11, is recruited so precisely to a double stranded break that nuclease cut sites can be determined with single-base resolution. DISCOVER-seq is applicable to multiple types of Cas nucleases and provides an unprecedented molecular picture of events that precede repair of the affected sites. DISCOVER-seq furthermore detects off-targets in cellular models and tissues.