CRISPR/Cas9 is a promising tool for genome-editing DNA in cells with single-base-pair precision, which allows novel in vitro models of human disease to be generated—eg, in pluripotent stem cells. However, the accuracy of intended sequence changes can be severely diminished by CRISPR/Cas9's propensity to re-edit previously modified loci, causing unwanted mutations (indels) alongside intended changes. Here we describe a genome-editing framework termed consecutive re-guide or re-Cas steps to erase CRISPR/Cas-blocked targets (CORRECT), which, by exploiting the use of highly efficacious CRISPR/Cas-blocking mutations in two rounds of genome editing, enables accurate, efficient and scarless introduction of specific base changes—for example, in human induced pluripotent (iPS) stem cells. This protocol outlines in detail how to implement either the re-Guide or re-Cas variants of CORRECT to generate scarlessly edited isogenic stem cell lines with intended monoallelic and biallelic sequence changes in∼ 3 months.